I keep seeing adverts with people wanting to exchange X for Y. I want to do that myself every now and then.

What if instead of in adverts, players could put it in a swap meet. Put your item/items there, and add things you'd exchange it for.

So I could say "want hel rocks, have flowery rocks or snow fort.." or "have hel rocks, want flowery rocks or snow fort..."

It would make it easier to swap, because not everyone looks at the adverts at the right time, and also it could be up forever until swapped. That way we wouldn't need to remember to renew adverts or hang out in sales. Well, maybe there should be a one week time limit, but you get the idea.