All my Sedo sales paid pretty fast, except one, a non-payer for a $4500 domain they bought. Sedo typically gives 7 days for each part of the transaction to respond - in other words, they make an offer, you have 7 days to counter, or accept or whatever; then they have 7 days to pay, etc. Sedo also asks/allows 'extensions', so even after the 7 days is up you can still make the next move; this happened to me last year while I was out in the boonies and only coming to town every 7 - 10 days; I missed a couple bids, they timed out, but I was still able to counter or accept them; however if I accept the bids after that 7 day period, the buyer was no longer under any obligation to honor their offer.
In the one instance of a non payer, after 7 days Sedo asked me what I wanted to do. I could have extended that period, they are open to extensions, but I just said to cancel it. They cancelled the transac, blocked the buyer from making any more bids on domains (but didn't delete his account, which I think should be mandatory, as well as blocking his ip), and sent me his contact details.
All other sales have gone smoothly for me at Sedo, and most buyers paid within a day or two, not waiting the full 7 days. Oh, except another one years ago, guy bought a domain for $500 but didn't make the 7 day deadline for payment. I said to cancel the transac, a week later the same buyer hit the buy now button and it went through fine. I didn't ask Sedo at that time why they didn't ban the non-payer after the first unsuccessful transac, but it worked out in the end after his second bid, ha, so whatevah.