Conklin & de Decker will give you all the numbers you need.
Buying a used helicopter has many of the same issues as buying a used car, may look good, dog underneath. You could also get a bargain.
Why not buy a Robinson after 9 overhauls, each time you get almost a new helicopter!
TTAF may be deceptive, consider the number of starts / cycles / landings / sectors. May be a better indication of potential stress in the airframe. Also consider previous owners and what that aircraft has been used for.
Ultimately due diligence should reveal potential problems.
Good luck with that!