I think money could be the the xp you get and auctioning is a great idea. But i also think there should tpa allowed
How about instead of using money, we could use xP, like someone auctions a sharpness X diamond sword for say 4$ but we could change that to 4 levels, know what I mean?
No support. Auctions on OP would be dumb as you don't gain money in the game and you can get mostly everything in kits or killing someone so it's really not needed. But on the other hand I think there should be a Shop where you can buy stuff and use your EXP Levels.