There was a line in "Bad Teacher" where the gym coach asked the bad teacher "Have you ever considered getting into another line of work? ANY other line of work?" That applies here, because that tech should be looking for work in some field other than computer repair.

How do you miss a disconnected SATA cable during your initial visual inspection? Answer: He never did one. He wanted to run up a tab, which he did, possibly following orders of the owner. Had it been me I would have reconnected the cable, rebooted, called you and told you to pick up your computer and have a nice day.

At the VERY least they should be refunding you what you paid them for doing work that did not need to be done. I doubt you will press them because you are probably a lot nicer guy than I am, but if I was in that position I would be writing to newspapers, ripping them on every blog I can find, and picketing with a thick stack of documents explaining that they are the worst techs in the history of silicon.

What they did was akin to you bringing you car in for a brake job and them painting it and charging you for the paint job. Awful work to not do a visual.