Machine
A jointer flattens one face of a board and squares an edge to it, so its two tables have to be flat and in line. To check, lay a straightedge on the outfeed table so it reaches at least 2 ft over the infeed, and slide feeler gauges into any gap. Old jointers here run from Craftsman's 6-1/8 in jointer-planer to 8 in long-bed machines from Delta, Powermatic and Walker-Turner. Wider and longer is better for long boards, and an 8 in Delta or Walker-Turner shares knives and cutterheads. Don't buy one without its spring-loaded cutterhead guard. The fence should lock square and the tables should slide smoothly on their ways.
6 models we cover.

Delta
Jointer$500–$1,500 typical ask
4 on eBay

Delta
Jointer$2,000–$2,000 typical ask
2 on eBay
Powermatic
JointerWhat to check before you buy →

Powermatic
Jointer$2,200–$2,200 typical ask
1 on eBay

Craftsman
Jointer$160–$160 typical ask
129 on eBay

Walker-Turner
Jointer$600–$600 typical ask
2 on eBay