How do you go about making your GAs as fair as possible?

Depends on the game I give away.

If it's a decent game I would like to be played, I set it for LVL4 or 5. With every level going down I care about the game less and less. LVL0 and 1 I use only for games I couldn't care less but also don't need laying around my library.

If it's something really good I will use groups or wishlist. Personally I don't want to deal much with checking every winner.. So I just go by increasing level and going group route for good games and hope for the best.

regardless of the GA-specific clearly stated rule that excludes them from entry (like winning more than a certain amount of games on SG)

There is no such thing as "GA-specific" rules. There is only the official rules of SteamGifts. I don't read every description of every public giveaway I enter, mostly just the ones of invite-only giveaways during puzzles, trains and events. I only make sure I don't enter for anything I already own or don't want to own and I ask if it's ok to enter if I already own parts of a package.

As for my own giveaways: I use a minimum level of 4-5 to reduce the amount of bots / autojoiners and I blacklist accounts I don't want to join my giveaways for some reason.

I also check my winners via https://www.sgtools.info/activation and https://www.sgtools.info/multiple-wins. As long as they don't violate SteamGifts rules, they get they key, even if I find something I don't like. If for some reason I don't want them to win another game of mine, I blacklist them.

I am not at the point of using whitelist and / or group giveaways, but that might change in the future.

I see a noticeable number of profiles with tens or hundreds of thousands of entries. How is that possible without bots? Especially in a short span of time?

Bot or no bot, every account just gets max. 576 points per day to spend. That is entirely possible by just visiting the site twice a day and spending all available points entering giveaways. Depending on how many points those giveaways cost on average, that could be 11 per day if every single one costs 50 points or 115 per day if every single one costs 5 points or even more for 0-4 points each.

Personally so far I am averaging about a thousand giveaways entered per month which would be around 30-33 per day.

use sgtools if you want to make specific rules. it filters anyone who doesnt fit your criteria.

You could make a group and define the type of people you want to win your games. I think group giveaways is the only sure fire way.
Other than that, higher levels or creating sgtool giveaways with custom entry requirements will help a little.

(1) no
(4) pure luck

Bleep Bloop. Darn, no hidden giveaway. 😂 I usually do group/whitelist.

sgtools did far more harm than good to this site

In my former puzzle creating career I've seen high level members, members of really good strict groups, ... who were somehow cheating the rules, one way or the other. Honestly, in the end, you're just wasting your time and patience trying to fight it. It's like DRM, only hurts the real people.

There is no perfect solution, only compromises with flaws and failures.
I once did some sort of "casting" to find a deserving winner for a Crusader Kings 3.copy. The result wasn't bad, as the winner played it for 42.4h.

For greater gifts that mean much to you, I simply wouldn't rely on SG. Make personal and direct gifts instead.

1, Yes there is, but idling games isn't a good enough reason not to gift the game.
3, It's not, unless you have and addiction to SG.
4, No correlation there. It's just that a lot of users that give away a lot of games have either been around for a long time, or sit in groups with small amounts of members giving them much higher chances to win.

1. No in that case.
2. You can try using sgtools to add extra requirements and reroll those that shouldnt have access to the ga
3. Entering hundreds or thousands is possible if you enter for almost all ga. Entering in a short amount of time mostly guarantees it is a bot tho
4. No.

I was questioning same about my winners. Then I stopped do giveaways and problems were gone.

The only solution that is consistent to me is moderated group GA's. Unfortunately, that is inherently a problematic answer because making it to these groups is not easy and I'm sure there are a lot of people that deserve to be there and are not, but any other alternative feels less than ideal. Whitelist is good because it gives you a lot of control, but goes back to the same issue with people who deserve a chance and you haven't found yet.

If I have to make a GA public, I absolutely won't use less than Level 2, but even that feels too low nowadays.

Let me emphasize a point some people made: # of entered GAs is not an evidence of using a bot at all! Well, it is evidence of "not having a life", but many meatbags (like me, 122k entries in 11 years) qualify! :D :D

That's because every account, no matter if "botted" or not, receives the same amount of points (24 per hour). Anybody that enters the site twice a day is able to spend all his/her points just as much as a bot. Bots do NOT enter more GAs then "no-lifers".

What bots are able to do is to enter GAs quickly (or anytime during the day); so, if anybody enters 20 GAs in the same second (or if they enter GAs every 30 minutes the WHOLE day every day), ok, that is suspicious.

(I actually would like to have a higher "minimum duration" for GAs for that reason, then bots would have no benefit at all in this regard... But that has been discussed, and folks thought the benefits did not justify the hindrances that come with the idea.)

depends really, if i gift a game i like i'd limit it to a group of people, if it is something i dont care i decide for every 10€ which tier it will get.

After weighing the pros and cons of public giveaways I prefer these threads for invite only giveaways which are essentially public but avoid bots to a certain extent:
https://www.steamgifts.com/discussion/Rl7Jo/dont-like-bots-post-your-random-invite-only-giveaways-here/
https://www.steamgifts.com/discussion/eOYPH/positive-thread-giveaways
My minimum level requirement is 2 because there are too many users not adhering to or understanding SG rules in the lower levels.

However as I wise up over time I lean more to whitelist and group only giveaways.

1. You see an entrant, which upon visiting their Steam profile, is clearly an alt that idles games, but you're forced per SG rules to send the key anyway. Well, is there a way to request a new winner?

There is no such thing. You can suspect someone to be an alt, but you don't know it, and of course it's not "clearly", just "in your opinion". No, you can't request new winner in this case, but if you have strong proof that this is an alt (no, "just look at it's profile" is not a proof) - you can report them. Technically if they are banned - you will get your re-roll, but problem is - user report resolved VERY slow, so unless you have some moderator as your friend and can ask them directly to review your ticket - no chance that it will happens during a week when you need to send the key.

2. Some/Many users use bots. Even if it's officially banned, it's clear as day that bots are being used.
The biggest giveaway (pun intended) is that they enter the GA regardless of the GA-specific clearly stated rule that excludes them from entry (like winning more than a certain amount of games on SG).
My question here is two-fold:
a) How do I prove this user is using a bot so I can report them?
b) If reporting them for whatever reason is frowned upon, how do I do what they do? lol

First of all, you CAN'T put some specific rules in giveaway description. I mean, technically you can, but users are not required to follow it, since extra rules are direct violation of SG rules. So, if you post some specific rules - every sane user will just ignore them, and it does not means that they are using bots. You can ASK NICELY - and then probably majority of users will do as you asked (but clearly, not all of them, and only thing that you can do to those who don't - is blacklist them, but then you will be bigger jerk than they are). As to your questions:
a) it's hard. And those who know how to do it - won't tell this publicly, because that will allow bot users to improve their strategies.
b) reporting them is fine, but asking how to do the same as they do is frowned upon.

3. I see a noticeable number of profiles with tens or hundreds of thousands of entries. How is that possible without bots? Especially in a short span of time?

Open site, enter giveaways for all points. Repeat twice a day. If you don't care about what you win - it's very fast. If you care - well, it sure takes more time and may require more than two visits per day. But anyway - it does not require much time or efforts, and easily achievable without bots.

4. Is there a correlation between giving away many games and winning or is that just pure luck (which I seriously doubt)? ? or is it users using bots again entering GAs en masse?

Well, it's moslty luck, only "correlation" is that with higher level you can enter high-level giveaways, which has less entries for obvious reasons and thus have higher chance to win. But making more giveaways to get more wins is just stupid and will never pay off. You can enter some closed groups that have much higher chance of win, but ultimately if you care about send/won ratio - you should stop making a giveaways and go to steamtrades instead - there you will achieve whooping 100% ratio - you will get as much as you give.

I'm sure all of these were answered properly, but my two cents.

1. Since it's difficult to prove someone is an alt or bot you can't. You can check via sgtools if the person activated all of their gifts. (If it's a bot chances are the keys were sold or activated on their main account.) This can be a resason to ask for a reroll.
   But many people here just enter giveaways to have a "+1" in the number of games and to farm cards to sell them (I guess?), they are not necessarily bots or alts just because of this.

2. a) You can try the method above, other than that not much that I know of.
   b) I don't think it's frowned upon. It's just some people like to play pretend and say there are no problems here. (Like bots, alts, etc.)

3. It is possible they are entering low point GAs for those sweet +1s.

4. Winning is random, it's up to luck. You have better chances if you enter giveaways with a lower amount of entries (like higher level, group / WL or quick GAs) and simply if you enter more giveaways.

What I have always done, is make my GA's the same level as my own. I've gradually worked my way up from level 1 to 6 and will continue to do so to 10. I also never worry about who the winner is or their motivations. If they entered the GA then they wanted the game, and I don't care why. It makes me happy knowing that somebody logged in to see the silly space cat gif :-)

The level needs to be at least two or three. Use SGTOOL, or a simple jigsaw puzzle to block BOT.
When someone wins a giveaway, confirm that the account has added games. If not, report it.