Riot gear works. I'm non-violent though. However, I am sneaky though to cut corners and use my athletic skills to maneuver in front of people when shopping or carry more than they can... I also do hide some items to wait for their colored sticker to go 1/2 off... Every edge helps.

I actually don't flip items from retailers that much, and you'll never see me waiting in line for a holiday event. I did make a killing during a large pharmacy merger a few years ago in my city, and also serendipitously grab some clearance things at retailers from time to time as an opportunist, but it's a recreational facet of my resale efforts these days.