Some companies make it a policy  

Back in the 1990s, after an incident involving a mechanic working at a remote location, PHI came up with a scheme whereby the pilot would *inspect* the mechanic's work and then sign off on it. The wording of the procedure said that the pilot would inspect the work and "ensure the completeness and correctness" of it. Now, this was troublesome. My license says "Pilot" not "Mechanic." I didn't want to be legally responsible (by signing my name and cert. #) for assuring that a mechanic did his job properly. Full stop. I objected to the company, who basically told me to pound sand. So I called the FAA. They put a stop to it.  

PHI revised the procedure into what they called a "Compulsory Check." With the pilot watching, the mechanic would explain the work he did, thereby giving him an opportunity to catch something he did wrong.  It provided the "second set of eyes" while at the same time letting the mechanic double-check his own work. I was okay with that. My signoff was something along those lines - that the mechanic assured me that the work was done correctly. But I was making no qualitative judgment, which of course I cannot.

We're all in this together. I have no problem looking over a mechanic's shoulder as he describes the work he's just done on my aircraft. But don't ask me to make any legal determination if he did it properly.