I've bought lots of used dies, and yeah, I've seen the rings all gorilla tightened. Usually no lubricant on the threads, either.
I haven't had trouble from used dies- other than the tight threads, and often they need a good cleaning.
I am kinda picky, though... I examine them carefully, particularly for scratches in the sizer. And I stick to RCBS or Reddings.
The worst part about used dies goes like this......
You see a set of dies for 15$, Good shape, etc., sooooo ya say "well, that's a good deal, even though I don't own a rifle in that caliber"
You buy the dies, clean em up and put them away.
About a year later you run across a used rifle you don't need at all.... but, ya already got dies for it.....
A set a used dies ends up costing you 3 or 400$