I am in the same airplane, my ass is in that airplane. The fact that my life is at stake. That assures the same thing I request from him. If we fly together, our lives both are there.
I personally know on mechanic who will never again fly because he had a horrible experience on a post mx flight due the fact that this particular pilot was a real i.d.i.o.t.
Any how, to got back to your original question and I can only speak from a EASA land standpoint - a certain amount of trust is required or you need to have a freelancer working for you with the necessary credentials to check and recheck what they do in mx.
I for one think that I can trust in certified stuff and then I check whatever I can. We use a well reputated mx organization, who might not be the cheapest.