Not certain how they're getting by with free installation and I've never been in or worked for a shop like that one though I've often thought I'd run one similar to that. Can't understand when a tune up is 75, you buy brakes and the brakes are an extra 10 per to install on top of the tune up, same with any other part but I get when you just buy brakes and the shop wants a small install fee. The one that always gets me the most is when you want to order something, they want the money up front and there isn't a discount. Shop is basically getting paid extra to just be a middle man which is a waste of cash to me. I'm something of a bargain hunter and haven't found shops that really offer comparable pricing so I tend to buy online, if I needed someone to install for me I could easily see being less of a bargain hunter and more of someone who shops around for free/cheap installation.
I will say with disc brakes, I just swapped my kids' bikes from cable to hydraulic and the total time for 2 bikes was an hour and that was only due to not having an air compressor to get the grips off quick or easily nor a replacement set to just cut the old ones off which were too new to replace anyways.