I just find out that you can unlock set Achievements on Steam buy lending a set from someone, activate it and than give it back.

Can I create a topic on the Trade subforum, to ask people to trade their sets, so I can activate the achievements and give them back?

Hi,

This sort of thing just happened recently and sort of went horribly wrong. It wasn't a scam, it wasn't someone being shady, it was a game mechanic screwing people over. The way packs work (different from sets) are that they are no-qi and can be traded while still in the pack. QI being the amount of games played, the amount of qi for items differ. For the game to give you the achievement, it needs to recognize all the items in the pack. So the two people did the deal, items were traded and unpacked, and then tried to trade back but couldn't. Unpacked packs put the qi limitations back on the items individually. So someone who only had 1000 qi could have a Vortex pack, which the items individually require 10,000 qi. I think you see where I'm going with this.

To answer your question now:
Keep it out of the market. This horrible example I presented was a real thing that happened and with it, Market Squad members do not want it in the Market boards. I wouldn't be opposed if you made a thread in Rapid-Threads. You can also ask around in Discord. Just remember to be safe and honest. Provide some type of equal value trade when doing it so everyone is safe even if you're just holding the items for a few minutes just for some achievements.