i think it's a relative term... 'too many' b/c we've(general public) all seen engines that 80k miles on them that run like crap... but, we've also seen engines that have 200k miles on them that run great. depends on whether or not is was taken care of.
I would take it to a trusted mechanic and let him look it over... see what he says... ask the seller if any work has been done to it, or ask what has been replaced, etc.
what ever you decided... good luck.