[SSLance]

I usually try to deal with the tire kickers as quickly as possible. Having to explain this type of situation just adds to that time and accomplishes nothing.

You aren't doing anything shady and it isn't going to cost the buyer any more once he realizes you are just an agent on the sale of the car. I'd get the fish on the hook first, weed out the tire kickers, then when it really comes down to it...explain who the seller is and how the rest of the deal will be accomplished. By then they already want the car and it won't be an issue.