I think the Proline is the better boat, the Yamaha ox66 is a great engine, but I'd be curious on the hours on both (I think the Yamaha has 400 if the one off Craigslist). As stated by others, both are a bit high. At that age, new engine could be right around the corner for either, so you're potentially paying 15k for a 11 year old hull and a trailer.
I actually wasn't impressed with the new Scouts when I shopped a few years ago, but it could have just been the half-a$$ layout trying to squeeze a toilet in the console.
I'd keep looking, although probably not what your buddy wants to hear.
This one is a 19k and more than you listed, but seems to be a much better boat for the $:
http://boston.craigslist.org/sob/boa/1751308567.html
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