Re: 1976 85 hp evinrude
Completeness, is it all there, including the remote control with wiring harness? General condition. How does it look. nice or pile of doo-doo? Signs of ovrheating, is the paint on the powerhead burnt or discolored, any wires melted where they touch the block or heads? If you get this far, and the seller allows it, pull the plugs, looking for any signs of rust in them. Then check the compression. Check the oil in the lower unit, is it full and free of water?
The things I just listed are the minimal basics. If it fails any of them, figure you are buying a possible money pit. If it passes, can you take it for a test run? Or does it run at all? Then there is the Judge Judy question, "Did you have a mechanic look at it?"
Bottom line: You pays your money and you takes your chances. How much are you willing to risk?