I can't believe how many outfitters leave their name on boats they sell to the general public. I think that if you run reaches of river they're permitted on, the boat can still be counted against their permitted allotment. This is why when the guides borrow a boat for an after-work run, they put duct tape over the outfitter's name. Not only that but I've seen some pretty embarrassing crews on boats that had an outfitters name on it.
Maybe you should photo of one of your buddies puking over the logo and send it to the seller with the threat that you'll post it all over the interwebs and Youtubes unless they remove the logo professionally (like he said he would)...
Good luck getting the logo off,
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse