cards which aren't marketable anymore

i did trade away all non marketable cards here https://steamlvlup.com/levelup
hope thats allowed that i post it and bought with the points full sets, but there are less sets than usual ,maybe because of incomming summer sale
Maybe some other users have a better site for that ,lets see ^^..

There are some websites that allows to trade unmarketable cards with other people, or even on ST, try see if someone wants it.. Is better than having 6 gems imo

Advertise on the game's trading forum. Lot of two of yours for one of mine traders (gougers) on there though. If you want the badge I suggest you try the 1:1 Trader's group https://steamcommunity.com/groups/honestmerchants
If you join there is a section called "open inventory" where users are happy to trade cross set trades using Steam Card Exchange values.
I also use the Dead Items group..users all want removed cards to help craft badges. https://steamcommunity.com/groups/deaditems
Sadly, the 2 for 1 gougers are moving in on this group as well.

Good luck, trading removed cards is really hard work.
Edit: Yes, you can craft the badge, even though the game is removed :)

turn them into gems, no point in wasting time for some cents.

Just deposit on steamlvlup .com and buy some badgs !!

the only real option is to turn the 3 cards in 2 gems each, right?

Even that takes more time than it's worth. I just don't bother with them at all.

but I'm also not able to get a badge from them

You can still trade with people to get the missing cards, but want my opinion? Don't bother. Not worth the time/monetary loss.

You can create booster packs to try and complete the set.

There is a userscript that will match you up with missing cards and then you can badge them once you have your full set and you usually get a 90% off coupon for some probably crap game that might have cards.

SteamTrade Matcher Userscript - automatically add cards to trade

Those cards can still be crafted for a badge, assuming you get remaining cards to finish it. Matching is not a problem, there is a lot of people with them too, I heavily recommend SteamTradeMatcher for that, or even better option - my own ASF STM listing.

You could now ask how do you get remaining cards - well, in the same way how you got your 3 current ones. It's not like you're losing anything, that convert button is not going to disappear anytime soon.

And there is a lot of people like you who are after the same thing, so it's always possible to trade them away for something you actually want, or get remaining cards from somebody else in similar situation like you who only owns half of the set.

In any case, converting cards to gems is not worth it at all, even for the absolute worst games on the market, including banned ones. A set has a standard value of between $0.20-$0.30. If you want to convert your card from average of $0.02-$0.03 into $0.0045, then that's your choice :3. Even the cheapest cards never hit the absolute bottom, this is different compared to e.g. emoticons or background, where their value of 10 gems is often better than $0.01 you can get from them, due to fees alone.

Still, up to you. I'd definitely not gemify them.

Trading is too much of a hassle, I just turn them into gems when I get them.

I'm collecting dust with them in my inventory.

View attached image.

Thanks for all the answers
I really like a clean inventory, (hate those coupons as I have to wait for them to expire to get rid of them) so just have them sitting in my inventory will annoy me. Yeah, I‘m strange but I like my virtual stuff to be clean and organized (unlike my real life)
Need to look for these trading options, people posted

There are a few trade bots that allow you to trade unmarketable cards from different sets against each other at a 1:1 ratio.

Vanilla bot is one of those; thanks to this one I've managed to trade the sets I had few cards from for cards that helped me complete a number of badges.

This group lat's you try to trade non-marketable cards / items for other non-marketable things. That way you might be able to complete a set.

Mine will gather dust until they die as nature intended.

I collect them, try to get the rest for a badge and when i have more cards then i need for 5 badges i trade the rest away.
And i trade sometimes, with steam friends, there unmarketable cards against my, cheap, ones that are marketable. For me it makes, mostly, not much difference because i can make the badges from any set and they can sell the marketable cards when they want/need wallet.

[I am known by my steamfriends for taking/accept the don't marketable cards by trades. Mostly with a 1:1 card trade, sometimes i offer csgo skin stuff that collect, mostly, dust in my inventory]

All is better then make the cards to gems