welcome to the forum.
If the bikes you are interested in are vintage bikes, put your inquiry in the section dealing with the value of vintage bikes.
If they are current models, then put your questions in the section of the type of bikes your checking out, ie:
road, commuter, hybrid etc.
If you are unsure, then in the general cycling section would likely work.
In general, with used bikes, the market in your area and your personal taste determines the value, whether it is a good deal or not will be up to you. We do not each value the same things.
New bikes is a whole 'nuther story....