Yes sure.
You can sell parked domains but do not make hyperlinks to the domains -> this would be considered potential traffic inflation
Rules #32 says that you cannot buy or purchase parking accounts. Scammers try to buy established accounts as a backdoor to defrauding parking companies with fake traffic.
Plus, people have tried to "buy" the ability to park a domain on someone else's account. They'd mainly do this because they were banned, most likely because of click fraud.