I've been a "
treasure hunter" for all of my life, haunting junk shops, flea markets, auctions, yard sales, estate sales, etc. After more than 50 years of this, I have come to understand a few things.
The first and most vital thing is, you must decide
WHY you are looking for used tools
(or any other used items).
Some folks love to slowly gather up bargain-priced items over many months, and then eventually resell them
(hopefully for a profit). Other people
hate that.
Some people really appreciate older high quality tools, and enjoy having them in their tool box. Others are ashamed of anything which is not the "
latest thing" in perfect condition.
A few folks want tools just for collections, which will be painted or plated, and hung on the wall or otherwise displayed.
Some folks are trying to build up a
working collection of premium quality USA-made tools, without spending a fortune for them.
(These folks are willing to wait a while before their set will be completely filled out...if ever).
Other folks hate all that, and prefer to step onto the tool truck
(or into Sears, or wherever), and simply open up a line of credit and get all the premium quality tools at once...
and they are willing to pay for it.
Other folks don't like that at all, and hate paying lots of interest.
Some folks cannot stand it when their tools are not all the same brand, in matching colors, etc.
Others prefer really good tools which they bought at a bargain.
NEITHER SIDE IS WRONG...
it's just personal preference.
So,
WHY would you personally be shopping for used tools?
Using me as an example...I am not a professional technician, so I cannot justify going deeply into debt or exhausting my bank account to buy tens of thousands of dollars of super tools all at once.
My vintage tools are just as interesting to me as the vintage cars I use them upon.
I LOVE going to yard sales, auctions, etc--and I love driving around, hunting for great bargains. It's not, "...a waste of a Saturday," ...it's a great day and I'm enjoying it fully! Hunting tools is great fun for me.
Old super high-quality USA-made or European-made tools impress the hell out of me. I like having them in my box--especially with a little wear and patina--whether or not I use them very often.
It's no problem for me, as an example, having a set of premium-brand sockets which is missing two sizes of that brand
(I have lots of other sets of most tools, and can almost always find the tool I need. So what if it isn't the same brand as the socket set I was using a minute ago?) In fact, that's kind of cool. It
gives me something specific to hunt for, and keeps me motivated to dig through rusty tools and old tool boxes.
I like selling stuff on eBay, and I set up a booth two or three times a year at regional flea markets. I love haggling and negotiating with other buyers and sellers of all kinds of stuff. And I like it even more when I'm selling items at higher prices than I paid for them.
But other folks would rather take an azz-whipping than have to, "...haul a bunch of junk to a market and sit with it all weekend, arguing with people over prices." 
I hope one day I will have a fabulous collection of super-quality USA and Euro-made tools, with very little invested. And I'm willing to work for it, and to wait on it.
(In fact, in a perfect world I'll pay for most of it by selling the other tools I buy in those big "package deals" I'm always making.)
In short...I'm enjoying myself. But other folks can't imagine what the hell is wrong with me!
You've already been given a great list of tool brands by Bolster and others, and gotten some great hints. I'll give you one more, which I came to learn this year:
Tools which are marked with sizes and "Made in USA", with no brand name may be GREAT to work with, but generally speaking they have no more value than the Asian import tools.
Now, armed with all this information, you need only decide why
you want to learn how to hunt for used tool bargains, and then get going!
Good luck!
