It depends on the shop, but as long as you appear serious about buying most would let you ride around (some will even let you borrow the bike for a day with a minor deposit). You don't need to ride on a trail to test a bike. Fist of all, just feel how it fits you, are the dimensions comfortable, etc. Second, pedal hard sitting then standing, how does it feel. Then try to go over some bumps and stuff, are you happy with the feel of it. Most bike stuff is very subjective, I always say go with what feels best to you and is made by a quality company.
