I had a similar experience with a plumber. Normally, I would have no clue how experienced the person was, but this particular person kept "missing" certain parts and had to make 3 trips to the hardware store! He only charged me for the first, but, clearly he didn't know what he was doing.
In the first case, the repairman came, fixed the thing in 20 minutes, seemed competent, and I gladly payed him.
In the second case, the company sent an inexperienced employee, who couldn't figure out the problem, and spent 2 hours trying everything before finally deciding the most expensive component needed to be replaced. I was very unsatisfied, especially since they charged me for all the seemingly pointless troubleshooting time.
So maybe it's not only important to make a lot of effort, but to also appear competent while working?