Here's advice from The Truth About Guns.
Don’t be afraid of used guns, but maintain a clear head while shopping. Depending on where you go, you’ll get to see and experience all sorts of nonsense. I’ve heard blatantly wrong information and occasionally dangerous advice. I’ve seen absolute junk marketed as new-in-the-box. I’ve also bought good pieces at good prices, so can you.
And another from Policemag.com, with advice that goes double for non-LEOs.
Buying a used firearm for duty or off-duty carry can present liability issues. If you have an accidental discharge or shoot someone in the line of duty, you will have to answer some very probing questions about the gun. Was the trigger worked on? Was the safety tinkered with to make it easier to use? You get the drift.And from Gunsandammo.com, which offers a great piece of modern advice and has some interesting comments below the article.
We live in the age of information. There’s no reason to start shopping for used guns without some idea of what a reasonable price looks like.I'm also not afraid to get experienced help in assessing a possible purchase. Even someone who doesn't have an armorer's certification can put another set of eyes on a gun and help decide if you really want this particular example or you want to keep looking.
H/T to SayUncle.