I hit the Estate sale scene here regularly. I always come across old power tools like sanders, drills, etc. You know, the old silver cast aluminum stuff from the 40'sand 50's. Is any of this stuff worth using?
Some is, some isn't, and some is down right dangerous to use. if it has a metal case, and does not have a grounded plug, I would either pass or upgrade the piece to grounded, which may or may not be a pain.
It takes some time and practice to tell the junk from the gems, so go slow and don't get too deep into the wallet unless you know what you are getting.