Yeah, I've come across that, but if you have a valid ID and driving license you should have no problem. Cash in hand will also grease the wheels - you don't have a cat in hell's chance of getting credit. If there is a problem, just take your business elsewhere - I'd say 50% of scooter shops freak out at the sight of a foreigner, and the other 50% are quite happy to make some profit even if E.T. rolls in wanting to buy a Goldwing.
btw don't get a 50cc. They're not much cheaper, they pollute more, they're not so efficient, and they're less fun to drive. They're also downright dangerous if you can't keep up with fast traffic. Get a 125.