As for the GS: I wouldnt like a complicated model that includes amount of time player is on the team, maybe role of the player (star, starter, backup...) Just keep it simple, so everybody can understand what this is all about, for example: the first unsuccesful sale should result in a -1, second -2 and third should go directly to GS 4 or even 2. I imagine a player wouldnt be very happy knowing the team would like to get rid of him and at the same time nobody is interested in buying him.
Maybe you noticed that we both are/were looking for a PF - and with all that players out there we both placed bids on the same guys unfortunately I had to let go of the Spaniard you bought (good luck with him!) :( - if you look for a PF with a salary over 35k you will see that most of them are listed at too high prices and wont get sold anyway thats not the way auctions should work.
Maybe BB could add a "Best offer"-function like it exists on eBay, where you can offer the seller your price and then get the player sold for this amount.
Another possibility would be to introduce the "dutch" auction - players start with a high bidding price, which is lower until the first owner places a bid and gets the player.