My small experience in having them look at mid grade cards again was interesting.
I asked in person at a show about two cards I thought were better than the grade, both T206s, one a 40 the other a 50.
The 50 had a tiny flake of paperloss on the corner and on the front, less than what's missing on most corner wear. ----It also had a
very tiny crease on the left edge that I hadn't seen. That was what put it in the 50 category rather than higher- like maybe a 70 or 80.
The 40 turned out to have an erased pencil mark on the back. One that I had never spotted in all the time I've owned it, 30 years +
Neither would have bumped on a paid review.
I can't say about the impression the standards are slipping. The standard says a tiny crease/wrinkle is ok up to 70, but I don't recall seeing one. And of all the cards I've had graded only two get a grade I thought was high. Oddly, they are a couple of the more expensive cards I've had done, one I personally think it's a full grade high, the other maybe a bit more.
The modern stuff I've graded with them didn't do well, but isn't worth redoing.
Steve B