In a car and running, I myself would be ok with the decent results of the comp test and hearing it run (cold and warm) both.
Personally I think 500 is a lot for a used engine and most of the (good) ones I see are between three and six.
When I bought my car I didn't do a comp test, but it ran ok on all 8 and didn't smoke and had good oil pressure.
The last thing I told him after I had looked it over and it was nice and warmed up was if I stuck it to 6,000 RPM and it didn't start making noises or blow up I would take it.
He said "go ahead" and I did.
Been driving it for over two years now and 4 trips to the CA coast and back at 80-100 and 11 hours each way.