This is a post I made in a similar suggestion a while ago, I'll copy-paste it.
I think an auction system should be implemented. When I was a child, I played a game called Neopets, that had one that was very good.
The auction system should be done in the forums, however.
If you want to auction something, you choose the starting price, minimum increment, and time (anywhere from 30 minutes-2 days)
To bid, a player MUST have the money, and CAN NOT withdraw the bid after it's done. When the auction ends, the player that wins the auction will get the item, and all the others get their money back.
I believe this would affect the economy positively, and lower level players would also be able to participate in lower level auctions, for example, a level 73 venusaur the owner used in the elite four is auctioned, and players that just got the fourth badge might want to bid on it up to a value of probably 10-20k.