if it is PPS (pay per signup) IMHO all the webmaster could ask for is a flat fee per user - just as a car dealer guy who sells the car gets commision on that very car he sells - and not on the upsells like window washing fluid, service checks, new wipers and what ever else is sold in that car dealership

if however he "owns" the customer he brought - then yes he'd get a commission on every revenue...

so I'd expact the 35$ and nothing more on a PPS programm