there is obviously more to this with regards to your personal experience with BB as I am an Elite Plus member, buy a lot during the year and make PLENTY of returns, and am always greeted with a smile and a "thank you". Not once have I ever been hassled, treated like a criminal or banned..
I have some knowledge on Best Buy’s ban process. There are a lot of different factors for being banned by Best Buy (How many Returns were made in a time period, items returned at different store locations, was the same item returned excessively, price tag of item returned). Best Buy doesn’t ban someone just for a few returns as you said, it’s a multitude of factors that are considered. I worked in loss prevention for number of years and this is something that is over the course of time that acrrues in order to be banned from returning items.