Asking the price of the gun shows that you have the hidden thought in mind about buying it later on and possibly commit some crime.
The point here is I haven't committed any crime, by all means I was honest. This kind of policing to prevent future crimes isn't good for the forum.
I'll just go ahead and tell people that I'm interested in buying methamphetamines, and just in case they're a cop I'll tell them I didn't actually buy it, so I didn't commit a crime. I'll continue to tell them that it's bad to infer what other people's intentions are just because they appear to be buying illicit drugs.
This is not how logic works.