I only had 2 deadbeat bidders, I posted their details here. Since Sedo does not reveal their full contact info, such as email and phone number citing "privacy" concerns, there is little that you can do taking the matter directly, other than filing a lawsuit and having a bailiff deliver the papers to the address provided.
When the seller's full contact info is available to the buyer at the time of the bidding, the buyer's full info should be disclosed on the contract as well. Sedo does not do that as European privacy laws are extremely tighter than those in the US. IMO, this is just bs.