Both of my big Prestos came from garage sales. The county home extension agent will test pressure canners for free and has tons of recipes. Any new sealing rings or regulators can be ordered from the manufacturer or hardware stores like Ace or True Value.
I had heard about local co-ops doing that service. I checked with ours before deciding what to buy, and they told me they don’t/won’t test the pressure canners or parts. Said I’d have to send them to the manufacture for that.
I brought new.
BTW, around here garage sales got wildly popular about a decade ago. I used to go every weekend, and soon noticed that the prices were pretty high for garage sale stuff. Next year they got higher. Same with our local Craigslist listings - the people around here “pro-rate”, LOL. If they paid $100. used it twice, they want $75.