I've been around boats some in my lifetime but I may finally have the opportunity to buy one. It's a 1978 18ft Arrowglass trihull with a 90hp merc, dual console, motor has good comp (135psi) and runs good also has tilt/trim, has a trolling motor, livewells, fish finder, and comes with a trailer. All of this for only $1650. Sounds almost too good to be true; what do I need to look for when I check this puppy out? Anything in particular? Anybody ever owned or heard anything about these?

I'm excited, I hope it works out   ;)

My first thing would be the flooring and transom area to make sure nothing is weak.  Especially the transom area, if that is weak then it's not cheap to repair.  Try to ask the owner as many question about the history or the boat why he is selling it, to try and get a idea about the boat.  Like the boat I got, it is a 72 model, their wasn't really anything wrong with it, but he bought a runabout boat and didn't need the fishing boat anymore.

Some other things about the motor some other guys will have to give you advice and things to look for.

I'm not sure I'd call a 30 year old boat for $1650 too good to be true.  I knew a couple guys that owned those Arrowglass boats way back then.  If it's a 17 1/2 footer they were rated for a 115hp.  That is a wood constructed boat.  The odds are better than 50/50 that there's rot in the stringer system and transom.  If there is, the owner would have to pay me to tow that thing away.