I always pick up shoes that are of value. You need to look at the soles to make sure they aren't shot, but for the most part some conditioner edge dressing and some polishing can really make a difference. If the soles are shot or there are major defects just leave them, most people don't want a project.
Yesterday I picked up a nice pair of Allen Edmonds Cliftons that will get some conditioner over the next couple of weeks and polished up they will look great.
I once found a pair of shoes that I suspected of being high quality but couldn't read the label on the inside.
Once I paid my $10 for them and got them outside, I could just barely make out the words Edward Green.
I am still kicking myself, though, for leaving the shoes I found a couple of weeks ago that I now suspect were Grenson.