Glass canning jars, mill, funnels - etc. yes. The pressure canner? Well, yes - but you have to really kind of know your stuff before buying at a garage sale.
The CONDITION the items are in is very important, and if newbies try to buy without doing lots of homework, it could be bad.
I decided to buy the major stuff new and cut the risk out.
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.