If it's a pre-90s era....
Genrally they fall into 2 categories...ones that have been pretty well maintained...and those that haven't. The ones that haven't...there's probably not an area or system on the boat that won't need work.
Teak decks need to be in good shape and not leak, the window areas inside shouldn't show signs of leaks, sanitation systems upgraded since original, bottom for blisters/hydrolysis, fuel tanks for severe rusting.....
I'm sure other's will add to my list...my 40 was a POS...but a better POS than the other POS's for the same price and still 1/2 of the higher end, well kept ones.