Used boats - rebuit, rebuilt or new powerheads, etc

Been looking at used boats and I see that a lot of boats, especially 2000 and older, have had rebuilt or rebuilt powerheads, etc.  is there any hiearchy of concern with avoiding?  Should I just avoid altogether, anything rebuilt? Anyway I can easily tell that an engine may be getting close to needing to be rebuilty?  Sometimes I wonder if a rebuilt motor on an older engine wouldn't be better than one that has never had that....but I also wonder if it needed rebuilding due to abuse or neglect.  My brother has a 1990s model Astro with a Yama 150 and he has never done anything major to it but he is meticulous about maintenance and always stored it inside.

What about rebuilt fuel systems?