If I look at a gun in person, I bring my tools to measure the barrels, chokes, stock and trigger pulls. If I buy a gun at auction, I make sure I can return in three days, mostly it if the barrels are too thin but still three days right to return. If a dealer or seller refuses to have the gun measured, I happily walk away and count my blessings. I have stopped dealing with three dealers for just that reason. If they are afraid to have their guns properly evaluated then I will never deal with them. People are a lot more reasonable before they get your money, than they are after the get your money and then have to give it back.
I have a thousand plus dollars in measuring devices and they have saved me many times that much in bad purchases alone. Much more than that if I had bought a gun and had the barrels take off part of my favorite hand. Not everybody needs to spend that much money, but you do need to know how to get the information you truly need about gun condition and safety. Pay a gunsmith to closely inspect your purchase before you lose the option to send it back. Find a gunsmith to do this, even if you have to drive to his location. You could always have him accept delivery of the gun for you and have him check it out mechanically as a starting point.
Every single gun in my gun room has been completely evaluated and measured. I started out doing this years ago because my kids used my guns and I wanted to make certain every gun on the wall was 100% safe for them to shoot. Then it became an information thing in that I just like to know and make sure these old guns will be good for the next generation or two after me to be shot safely. I have a book which details all the measurements along with any note about things that I found or repaired. Those who are too far gone are deactivated, including a few family guns which have been used too long and are no longer safe to use anymore. Mostly those were typical farmer guns which got far more use than care.
