well you can check that stuff after you buy it.. ain't nobody dis-assembling my scope before they pay..lol I haven't even gone that far.
but all good things to check..
actually you would be surprised how much damage has to occur before viewing is impaired .. I once saw a badly dented, dust ridden scope with a big ol scratched corector plate..eeee gads was a poor scope, but image viewing wise you would never know it.
I think the owner said he got it free from a neighbor that dropped it moving. gives me nightmares thinking about it.