Biddance.com and GoodBiddance.com -- Biddance and Good Biddance
Biddance.com would be perfect; while a Brandable domain, it is also descriptive of what happens on an auction site: bidding!
And when you think about it, bidding at auction is a bit of a dance among bidders.
GoodBiddance.com, while a long tail domain, is a positive play-on-words for the term "Good Riddance."
So give a "Good Biddance" experience to your potential customers.
*These two terms are so brandable and interrelated that we are offering these two domains for one money!
The buyer will purchase Biddance.com, and once funds have cleared and transfer has completed, GoodBiddance.com will be transferred to the buyer, free of charge!