I used (and sold) via Domainlore for the first time this week, an absolute piece of cake, whereas I have never sold on Sedo in years of trying. In fact, this thread could maybe be a 3-way discussion to include Acorn, which also comes up with the goods.
Where the VAT issue comes up, it's easy to see that Denys initial efforts have been to say to sellers that the price is always VAT inclusive to make things simpler, but if the buyer is VAT registered and the seller isn't, then no legitimate VAT invoice can be issued anyway. I don't see that as a major issue for now, given that the transaction ultimately doesn't involve Domainlore, which gives the parties involved a chance to iron those points out after sale.
Turn to Sedo on the other hand, and as they're invoicing for their own services, they still don't seem to have this clearly defined on the commission side, something which must be irritating to anyone wishing to dispute this point with them. When you consider that Domainlore is a one-man band, and Sedo is a global organisation, then Denys site punches well above its weight!