How to tell if a bike is good before purchasing? Say there's no sales person in a bike shop and you are just looking for bikes.

The criteria would be a good bike to ride to work on side-walks(paved or smooth) and the occasional off-road on the weekends. Female user, small budget, but the bike should have a kickstand, a good seat, lights and a bell.

What are the things to look for before purchasing?

(In Norway, bikes aren't too cheap but the buyer doesn't feel comfortable buying the cheapest)
New bikes are usually good to go. The LBS (local bike shop) will usually allow you to bring it back after a months time in order to readjust and tighten things that may have come lose. Ask about whether this is supported or not. Also ask about the guarantee and its exact details.

Also you could ask for a test ride (even in the parking lot) to make sure that the bike works.

Generally the bike should:


have inflated tyres
have no loose parts (grips, bars, saddle, cranks, pedals, wheels)
have working brakes
be able to shift gears smoothly