Go over it with a fine tooth comb, test drive it, and have the motor checked by a mechanic if you can.
I bought a 98 Nitro 700LX bass boat 2 years ago. It’s my first boat and it has been nothing short of perfect for me. No motor problems, no other issues with the boat. Only issue I’m noticing is my steering is a bit tight. But the cables are the originals and probably need replacing.
Long story short, someone is always going to have something bad to say about something. If you like it and it passes your inspection, I wouldn’t worry about the fact that it’s a Nitro. There are more people that are very happy with their Nitro’s than there are people always ragging on them.