When you see a listing for a outboard motor you would like to bid on, message the owner for a compression reading  on all cylinders, if not in discription.almost all motors from 5hp to 150hp will have 100lbs.or more,the important thing is that all cylinders read the same,if 2 read 120lbs and one is 100lbs the motor will still run but the 100 lbs cylinder has a serious internal problem that will cost you a good deal down the road. do not fall for the person telling you they do not have a compression gage, any one who buys and sells motors has one,or should have one.hope this helps some one.  Ben