Welcome to CGN. We actually have a milsurp section where experts like to hang out and offer advice of this type freely.
I'll give you a couple of pointers for the Garand to get it started. Generally, you're going to need a bore light to inspect the rifling as the rifle is a semi auto. Look for strong rifling and a shiny bore. You should probably get the headspace checked by a gunsmith if possible, and generally just look for pitting on the receiver area-- bascially what you would look for in any rifle really.
I'm sure the experts will weigh in soon.