My father-in-law has a best friend who owns a dealership in St. Luis, MO and the only way to make any real money is to sell high volumes of weapons. Those who cheat you are those who do not sell many because their prices are too high. If a dealer is selling it for more than $40 - $60 over cost, then you are being raped. Many years ago when I was in the .mil I worked a part-time job at a gun shop and they too only charged on average $50 over cost on new stock. Otherwise, they could not sell anything.
Also, many dealers out there have no real knowledge. I asked one guy at a show for a 16" barrel and he brought me a 14.5". I looked at it and I could tell it was not 16". He insisted it was and we measured it. He didn't even know how to measure it properly. I schooled him in front of other customers and he lost business. If you are a dealer and you do not know your stuff, get the hell out of the business. This guy could have easily caused someone to become a criminal if the customer did not know any better and thought they bought a 16". On that note, you as the customer are ultimately responsible for educating yourself.
IF you are not 1000% sure about it, do not buy it without researching first. In today's society with the advent of the Internet, there is no excuse in my opinion.