Buying doors

[JohnBishop]

Hi All,

  I am looking to buy some used solid wood doors.
Have you had any experience what to pay attention to?
I know I have to check the dimensions but I also wonder about the door handle. I think this is not standardised and I should also take those measurements into account (I reckon measure from top to the door mortice?

I think some old school wooden doors had the door handle quite high. OR should I consider replacing the door frame at the same time?