I met an electrician in a line to enter an estate sale. He made a habit of going to them, because people would have things on sale he could use in his business at a fraction of what he would pay otherwise.
Especially obsolete circuitbreakers
I have bought some of my best hand tools at estate sales. Especially if it is the second day of a two day sale. The company contracted only gets a commission on the things they actually sell. So, on the last day they are really motivated to get rid of anything no matter what price you offer them.
The other thing is old tools from the 1950s are made so much better than stuff today.