I didnt read every single post here, but I got the gist at the beginning. I used to work pretty high up as far as best buy's hierarchy goes.
First of all, to the original post, if the loss prevention person so much as touched you in an effort to restrain you, you have a lawsuit. They are in no way permitted to even touch your shoulder in an effort to restrain you.
Second you are fully granted by the law to walk out without your receipt getting checked. Just deny the request to have your receipt checked. Now yes they lose lots of $$ to internal and external theft, so if you are an honest person, in the long run as a consumer, it benefits you to have this process in place.
Someone had mentioned citizens arrest. First, citizens arrests are not permitted everywhere. Second, a Best Buy employee is not a citizen when he is working. He is Best Buy corporate and can do absolutely nothing in the way of stopping you. They must, MUST wait for the police to detain anyone.
If they witness you walk in the door with no product, take something off of their shelf, put it in your coat, keep you on camera at all times, and let you get past the last point of sale, then they can ask you to stop. No more. If you walk out, you walk out. Anything further, lawsuit.
Personally, Best Buy is a terrible company that deceives, cheats, and lies to its customers from the top on down (trust me, dont shop there).