Javelin, you are certainly correct on one count...you don't know how the engines were operated by a previous owner.
However, if they have made it to 800 hours (or so) without blowing up and sending bits through the cowling...it may well indicate that the previuous operator knew what the heck he was doing.
Example:
Some of the older folks here might remember the movie actor...Danny Kaye.
He based his Beech QueenAir B80 at KVNY, and I knew him quite well.
His B80 was bought brand new, and when he sold it, it had 2000 hours on the airframe...with the same engines as when delivered.
If a Hollywood-type movie actor (who happens to be a well trained pilot) can fly his geared/supercharged Lycoming engines for a long time without much difficulty, just what does that say for the 'new' brand of pilot who might blow 'em up on the first ten takeoffs?
I would prefer to call it..sh!t for brains.
