The shop should have replaced the chain and rear cassette or freewheel to stop the chain skip. They should have serviced the rear derailer so that it was fully functioning. Avoid that bike shop from now on.
Test riding is always a good idea. Can you find a bike like the one you rented for sale somewhere? Always test ride before you buy.
Last edited by rumrunn6; 12-01-09 at 11:23 AM.