Thanks Steve. Any tip that helps me avoid beginner-mistakes is much appreciated. I will be careful with Sonets. Or Crown-pressings for that matter.
With regard to vinyl-checking, I don't know. I've come across pretty scratched-up records that sound surprisingly good, and some clean-looking ones that turn out to have major issues. This Jubilee reveals no serious defects, looks unplayed even, but it is just awful. There are no clicks or pops, just a loud hiss that pushes the music to the background. I was not aware that this level of deterioration with an otherwise 'clean' record was possible.
That said, i was warned, so really no complaints there.