LICENSED ammo makers (new and remanufactured) are in business. They have standards, and they have INSURANCE.
They make some pretty good ammo. They don't make the best ammo
possible for YOUR GUN, but they try hard to make the best ammo practical for all guns in each caliber.
I was at a large Gun show and one shop had table full of handloaded new component hard to get ammo. I bought a box of .22 HiPower and it was loaded so hot the lever stuck on my 99. Never again.
In cases like this, the safe route is buy the ammo, and pull it down for the brass and bullets. It may have been "safe" in their test gun (assuming they have one, or even do that step) or it may have been a listed load somewhere that they just assembled without any testing. WE can't know.
And, yes, every horror story you have heard of probably has happened to someone. At a gun show one time, I found 6 boxes of "factory" .45 Win Mag ammo. I checked, 2 of them were. The other 4 were reloads in factory boxes. The seller thought they were all factory, that's what he was told when he got them. Actually opening the boxes and looking at the brass would have shown him otherwise, but who does that, right???
I do. Pointed out to him (once I found the first one) how the cases had clear signs of resizing. He was embarrassed, and a little ticked at the guy he got them from, by way of apology, he gave the 4 boxes of reloads at a cut rate price, for reloads.
AS a caution, if you find "factory" ammo at a gun show, and the factory box looks a little old, or shows more than just a bit of handling, check the rounds inside carefully. I put reloads back in factory boxes, myself, and usually labels of what it really I put on the inside.
So someone else doing that, or even not including a new label (cause they know what it is) can happen, and some of that could easily wind up a show. I've gotten ammo like that from estate sales. One time I found 8mm Mauser reloads neatly packed inside Marlboro cigarette boxes....
literally anything is possible...