Check for the Hull Identification Number plate - that will give you some more information. Here is a thread on what looks like a similar model to yours.
Looks like an early Thundercraft Titan- 15' trihull. Thundercraft was a builder that merged (or was taken over) by Cadorette in the late 80s- early 90s.
Looks about right with about the same vintage Merc. There were a ton of Trihull boats manufactured in the 70's/80's I hope your trade wasn't valued at to much.
