Re: 1996 Mercury 100 HP
I'd look a the bottom end fluid, make sure there is no water or metal shavings.
A good look at the electronics on the motor, check to see if its orginal, or have parts been changed. The general look of the motor. ie does it look like the skag has seen a rock or two. The prop? is it dinged, or chewed up. Ask about maintence, the water pump etc. A compression test is a good idea, but they can be miss leading, a motor can have good compression, yet have a bunch of other problems. Ask the seller if he would offer a warrenty?