Most of the things you may have read on forums can be spotted or caught during a field strip and inspection Before you put your name on the NICS form.
Tell them you need to inspect it before you buy it. If they won't let you Field Strip it yourself, ask THEM to show you how to Field Strip it and when it's apart, check the barrel for abnormalities (burrs etc), the RSA for that infamous 'Bent Disk' and ask them about proper alignment of the RSA during Assembly. Of course... check the sights and make sure they're centered, try Dry Firing, to make sure they're not trying to sell you a 'Mass Compliant' Shield with the heavier trigger
, etc.
My LGS knows I'm not going to buy a firearm that I haven't 1st inspected, so they expect it from me. When I got my 1st 1911, they went over 1911 Field Stripping and assembly differences with me, before we did the paperwork.
But like I wrote... If you take the time to inspect it before buying, you'll avert the problems you've read about.
Tell them you need to inspect it before you buy it. If they won't let you Field Strip it yourself, ask THEM to show you how to Field Strip it and when it's apart, check the barrel for abnormalities (burrs etc), the RSA for that infamous 'Bent Disk' and ask them about proper alignment of the RSA during Assembly. Of course... check the sights and make sure they're centered, try Dry Firing, to make sure they're not trying to sell you a 'Mass Compliant' Shield with the heavier trigger

My LGS knows I'm not going to buy a firearm that I haven't 1st inspected, so they expect it from me. When I got my 1st 1911, they went over 1911 Field Stripping and assembly differences with me, before we did the paperwork.
But like I wrote... If you take the time to inspect it before buying, you'll avert the problems you've read about.