Suggestion - Make people post something in the giveaway description.

So now every description will be like this: "20char 20char 20char." that's really helpful

why not exactly? its still against the rules yes? and way to be a dick when somebody's trying to give you something free if you did.

"No no, dont blame him for raping her, she was asking for it showing off her ankles like that!"
Your logic right there.

Then instead of "Delivery" write "How will you give your gift?" with "I have steam gift" and "I have steam key".

Well then, how about making the wording unambiguous?

"I am going to give away the following game:"
Drop down

"I want to give this game to:"
[ ] everyone [ ] group [ ] invite only

"I will give the game to the winner as:"
[ ] steam gift [ ] steam key via chat or mail

Essentially what your saying is the wording on the site is not clear enough. So, it should be made clearer.

Edit: and if all else fails, another checkbox on the giveaway confirmation screen.

"I declare that I have a giftable copy of, or a new steam key for this game, and the intention to give this to the winner of my giveaway."

If nothing else, that should stop people who don't know what they're doing. If someone actually wants to create a fake giveaway, none of this will help.

which is

A: still a dick

and

B: still against the rules((which exist for a reason)

so....

In other words, you admit it doesn't solve or change anything.

if the mods and rules(not to mention common sense and courtesy) saying not to call out don't stop people why exactly would a "potential faker" saying it be believed?
If anything isn't saying "IT ISN'T FAKE" more suspicious to these people?

Ok, but he was attempting to use your defination not his own, and even in your example this is people being dicks and breaking the rules, not people being justified in doing so because the (potentially reverse-)gifter didn't type anything and therefore was asking for it. your premise has no sense.

If you got your wish and there were forced descriptions even the "fake" would have them.

this would accomplish nothing if enacted, blames the "victim(who maybe id it wrong)"(and simultaneously justifying potentially harassing new users off the site) not the rule breaker calling them out, and worst of all it would be mildly annoying to everybody involved(which may even effect me at some point!).

Besides....RE: Calling out fake giveaways:

if you're right basically no effect. the (non)gifter usually doesn't come back to check comments, most entrants don't read them either, those who do can see just as well as you if theres something to suspect, and you didn't enter anyway so no risk of your points.

if you're wrong some new user gifting high quality may be offended or get the wrong impression of this community and go somewhere else as a result, or decide based off that experience to not send to the winner, or never gift again, or if they do they may be more hesitant do do so, possibly sticking solely to groups in the future(groups you aren't in).

wheres the up side to this? how do you "win"? even given that you will probably be more often right than wrong and that often even when you're wrong the gifter will just shrug it off anyway with no effect, it never works out to any gain and still carries the risk of loss.