I've bought used monitors.
1 came with "bruises". But at the time, it was originally $800 21" Planar, I got for $40.
It lasted 15+ years.
Another used 17" HP has lasted almost 20 years. It came with a bunch of other PC stuff for $50.
It is currently the display for my house security cams.
You can't put a definitive "yes or no" on "is it safe" for any used equipment.
Some are good, some not.