Well said TDD
Those of us in GA engineering see so many A/C that only come in for annuals as they don't want the expense of trusting their 50's / 150's to a 145 organisation, how wrong could they be? most of the exorbitant annual cost is going over and re-doing SB's / AD's and routine maintenance that may well have been carried out but has never been recorded in the A/C's history so as a certifying engineer you have to re-do the task to satisfy yourself that it has been done.
I'm all for customer participation but only on a verbal basis, i.e. keep the customer informed of any problems as soon as they arise and invite them in to take a look if they want and you soon build up a relationship of trust, but never would I let a customer work on his own A/C during a check. What he does to the A/C when he takes it away is his business, I have no control over that.
IO540
I agree your 50 hr inspection is little more than a preflight if done on the N reg, it is however a fair bit more involved on the G reg under LAMS. As an aside your friendly A+P is not doing you any favours if he lets you run the engine without cowlings for a leak check. Most manufactuters including Socata state run engine with cowling in place at 1200 rpm for proper cooling for two minutes then remove top cowling and check for leaks. Any ground run without cowlings can only be doing damage to your engine. Just a bit of friendly advise.
JB