Engine Hours Modified or reset

No

Were not talking about a small gas boat, but a boat with real engines (I assumed).
From what I've witnessed, used gas boats and small diesel boats are usually exported from the US and very well surveyed before final purchase.
It goes back to a engine survey that would show anything different from reported to real life.
Poor or no records from a seller, walk from or assume the worse.

AND, I may not have problems with high hours if there was a well documented operating & maintenance logs to reflect a properly serviced power plant with no abuse.

Other thoughts, but that should do.

not to hijack .....but...I seem to remember hour meters that adjusted the hours to the amount of RPMs the engine turned..true???

in other words ; if the engine idled for 1 hr, the meter would show 1/4 hr of use..

i believe they were on a Stevens i ran....meters never were up to my log records...also about the time DD was sold, conversation at a major truck sales and supply place were i got my oil/filters, was about the trucks depending more on the cycle count as opposed to hrs.

The old CATS that had a mechanical one off the tacho drive might have used this method.

Most mechanical tach/hour meters use a magnetic drive and are calibrated so that they read hours accurately at a specific rpm. Lower rpm will record less time, higher rpm will record more time. The difference exists because the drive consists of a spinning magnet that drags a disk connected to the indicator.

Recip aircraft typically use this type of tachometer plus a separate electric hour meter that starts recording at engine start. Maintenance is performed by "tach time" and revenue is charged by "Hobbs time" - so named after the company that makes many of the hour meters.

Increasingly trucks are fitting APU's as the per hour cost is significantly less than idling. And, 6-7000 hours on an APU is not unheard of.

Ah, the young among us;
Old mechanical tach's had hours display on the same display. Described as Marmot detailed above, crude for a marine engine but was pretty close to real time on the long run (200+ hours) and worked well thru it's life as a maintenance record keeper.
I have worked on a few boats with those oldies. As long as the mechanical tach cable was oiled and not whipping, worked great.

I'll stick my neck out a bit and say that most of the (pre-electronic at least) CATs and DDs had a mechanical drive fitting. An adapter was available to fit a tach generator to drive an electric tach.

Since mechanical drive cables were problematic when the distance between engine and tach got a bit long (depending on bends) most boats that placed the engine instrument panel some distance away installed the electric tach generator or used a mag pickup to read the ring gear.

No sharp turns in the cable and oiled once every few years. When they worked, life was good.