Rob,
Sounds a lot like my situation with the Cherokee. It wasn't making power, so despite an overhaul only 164 hours before, we went back inside with my local AP/IA to put in a new camshaft. We did not magnaflux the case, nor the crank, but all new bearings, cam, lifters, seals and safety's. While it is not a major, I feel very comfortable with the internals of the engine now. I personally worked with him to measure all tolerances and specs to the best possible spec. It is tight, smooth and pulls like a farm tractor now that we have the new muffler on it.
This wouldn't scare me away too bad as long as it is not making any metal (make sure the engine has a few hours on it before pulling and cutting the filter, and drain the oil through a coffee filter.)
Check at some nearby airports to get a feel for the reputation of the mechanic. I looked at a deal on a rebuilt bird in Wyoming a few years back. An A/P owner was the one who did the work. When I checked with a couple other local AP's for a pre-buy, they all declined saying the guy slaps wrecked birds together with non-certified parts and generally does lousy work, so I walked away. If the mech is reputable, then it wouldn't scare me off at all.