Turn used canoes upside down and sight along the keel-line. Once a keel-line is bent, it's almost impossible to straighten properly. A cloudy matrix tells the tale. Once delamination begins, it usually continues. Galled varnish, scratched gel-coat and surface cracks in woodwork are easily repairable.
Good canoes appreciate.
Bad ones do the opposite. You can't go wrong by buying a good used canoe.