Funny. I found and bought the same Wyn air gauge at an estate sale. I thought it was a manometer and was thinking of using it to check when my shop vac filter needed cleaning. I showed it to a friend of mine that used to work for TX Parks and Recreations and he said that he had used one before.
I've gotten pretty lucky at garage and estate sales. My wife goes more often than I do and she has learned what to look for that I would be interested in. We have found several really nice hand planes. Many of them are in rough but still salvageable condition but usually cheap. The best sales are where the wife is out in the shop telling her husband he needs to let go of some stuff.
(Warning tool gloat ahead.)
I've had some pretty big scores. One guy was downsizing and moving and so was selling all of his clamps. At the end of the day, I got over 20 Bessy K-clamps for $12.50 each. He was asking $25 each but when I balked he lowered the price because he needed them gone. I also got about 100 various F-clamps, mostly small 6", for just over $100. I bought several other things from him as well, including a couple of hand planes in excellent condition. One of my biggest scores was from a young guy who had just gotten married and needed to empty his garage of tools so that he could move to a house with a smaller garage and so his wife could park in the garage (must really be love). He was selling all of his relatively new power tools for half what he paid for them. None of the tools was more than a couple of years old. I got a complete Shark 24x24 CNC for $1200, including a stand and tooling plus several other tools for cheap.
(End gloat)
Unfortunately, many people selling these days try to use eBay or some other websites to try to set their prices. No one is going to pay that at a garage sale. As soon as someone mentions eBay, I usually turn around and leave because the prices are going to be ridiculous. What they don't seem to realize is that they cannot compare a walk in crowd looking for bargains to a national audience. Also, they have to subtract all of the fees associated with selling on eBay, including credit card fees and shipping costs. Those can easily add up to 15% or more. I've tried to explain this but most people who have this mindset are not motivated enough to sell so it is not worth the effort to try to haggle with them.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.