The Saltwater 150 does not store hours. There is no way to verify the actual motor hours.
It can be quite hard to determine condition from looking at a few pictures. Problems like water intrusion, transom issues, stringer issues, rotten wiring etc, will not show.
The motor being 25 years old has very little value. The trailer has some decent value if everything is basically solid and working. The SX150 is a great motor but again you can't judge its condition by looking at photos.The motor being 25 years old has very little value.
Who are you talking to? Is it the owner or is it a broker? There are a few red flags that I look for but two are high on my list: A really dirty , not well kept boat. If the boat was not cared for, the owner probably didn't do proper mechanical maintenance either. The second red flag is not cast in stone but always gets my hairs up
If an older boat like this one looks too clean, I usually assume it was detailed by a broker and that can be a problem, if issues were covered up. So look past the obvious and check the bilge, under the helm, anchor locker, hardtop mounting and welds, canvas if any, undersides of cushions, etc.
With regard to carrying 6 passengers; If you run into rough seas or rain, most of your passengers will get wet, Even on nice day, they might get wet. That may or may not be an issue but having a place to change clothes or wet bathing suits as well as a place to do one's business may be a concern. As mentioned, small tots like to nap and this CC is not built for that.
Good luck with your search.