Sedo are really bad when it comes to protecting sellers. They simply don't care.
The majority of my sales have turned out to be from non-paying bidders, and Sedo support just ignore you and say "we take every effort to contact the buyer".
There is a Sedo staff member over at another domain forum that is actually good, though. He looked into one of my sales that didn't go through and within 10 minutes he found out that:
1) The buyer had quite a few other auctions which he/she had won, but hadn't paid for.
2) Hence, this Sedo member compensated me by adding my domain to the featured category thing - for free!
This was, in my opinion, a great thing to do - Sedo should be doing this all the time. It's easy enough to do, although Sedo just can't be bothered.. (apart from this one staff member, fair play to him

)
I'd love to see Sedo fail, I really would. Unfortunately they're in a relatively monopolistic position, hence I'm thinking that their abusive actions (from not protecting sellers, to cancelling auctions that they think could have gone for higher) will go undisciplined.