Tom,
My invoice to the buyer is itemized, listing what amount I receive and what goes to Sedo. If Sedo has a problem with that, I suggest that you look for an alternative method of providing proof of purchase to the buyer.
When a transaction occurs through Sedo, your company is not "merely the marketplace" but acts as the Escrow handling the buyer's funds and the seller's domain. As such there is never a direct exchange between buyer and seller, especially since the contract hides the buyer's information from the seller until the transaction completes.
If the buyer has an issue with the invoice I have produced, itemizing the proceeds they should contact me. As far as I am concerned, I fulfill my obligation once I hand over the domain to Sedo. The invoice should be an option and not a requirement. I am not objecting to the invoice part, however per my financial advisor's advice I shall not issue an invoice as if I received a full sale amount.
Please understand that this is becoming a thorn in ongoing transactions as you've introduced this feature without prior warning. I expect that Sedo releases the funds immediately, otherwise I am going to be very upset with Sedo.