Well, unfortunately we can't do anything about that. The one good thing is that if the player is re-bought, his time on the club is reset to zero and it's counted as a transfer in the last 14 weeks, so if the player is re-listed shortly thereafter, the owner will get a lot lower percentage the second time.
With that said, it's permitted currently. I don't like it - I can see letting someone do it to try to rebuy their player if they didn't want to sell them or need them in case another player got injured, or if they set the wrong starting price, but using it as a "set a low price, then drive up bids at the end" tactic sucks. It's one of the reasons I also don't have a lot of sympathy for people who list players low and get 'screwed' if the site goes down - if you want to make sure a player sells for a million, you can list him at that. If you don't and he doesn't, too bad.