So my friend said he used to work as front door security at Best Buy a few years back (the guys in the yellow shirts at the entrance/exit). Keep in mind I am not 100% sure if these practices are still in place, or apply to every store. I'm just sharing the info I got from him.
Cameras: There are some blindspots in most Best Buys. However, he said that the only person watching the cameras is the guy at the front of the store, which was him. They did not have a backroom with someone monitoring them. And apparently, the screen he would watch the cameras with would only show ONE camera at a time, and it would change every minute or so. So the odds that the security guy is looking at the screen AND happens to be looking at the one camera that is monitoring you, I think is unlikely.
Lifting Methods: He worked there for about a year and only caught ONE person (not sure if people are just that good or he's lazy lol). It was a person changing price tags on TVs to get a cheaper price for a nicer one. They didn't even call police.
Security Tags: Didn't mention anything about them
As I said, this is info from one person who only worked at one store. Take everything with a grain of salt. But still... Given his tips, it seems that it would be rather easy to lift from Best Buy :)