...looked at where it was to be installed (above the stove like most microwaves) and saw that it was a cinder-block & plaster wall and said: "We only have screws to install in wood & sheetrock. Here's your microwave and we will refund the installation charge. Sorry about that, we are leaving now."

The whole reason I paid for installation was so that I wouldn't have to deal with installing onto that wall, dangit. Boo Home Depot.