yeah i know what you're saying but with a 2nd hand turbo you dont know how bad the wear is if an oil seal is blown. for example, my car would drop to almost 1 bar of oil pressure! (i took it off the road as soon as it did though).
that was after weeks and weeks of driving with a known blown oil seal, out of nowhere i had almost 1 bar of oil pressure.
on a friends car.. he was running quite rich as well as having a blown oil seal on his turbo, driving behind him it looked black. we only found out he had a blown turbo when we were replacing his fmic.
so with a 2nd hand turbo where you dont know the condition of internally, its hard to really trust if its in good condition. so like i said, look for warning signs, and dont ever take chances with low oil pressure or YOU WILL GET STABBED.