"I've seen fifties era 7.5
"I've seen fifties era 7.5's go for fifty bucks, then agian I've also seen a mint 7.5 never been run go for seven hundred and fifty bucks. Where does yours belong in value, I dont know, whats it look like, who did you buy it from, and is there someone out there that would give you your 175.00 back for it? It's kinda hard to see it from my house. There's lots of 7.5's out there, and getting one that "runs" for a hundred, or two, is pretty common place. What year is your mariner, have you investigated the condition of commpression, spark, and such things that can make or break the value of such a motor? How's the paint, to some peaple the paint is a good indicator of how well the motor has been cared for. Five hundred bucks sounds reasonable for a 15hp and they go for about that, or more. One thing is for sure, it aint worth a quarter if it leaves you stranded out in the lake. A used motor that seems to run good can and most times need a tune up, or a lower end, or a carb. After doing, or even worse having a mechanic do work on a motor could cost more than what you paid for the motor in the first place. Post the model number for your Sears 9.9 and hopfuly Graham with his library of manuals can give you the details about your motor."