The stickers (which I hate - free advertising and defacement - I've never used an authentication company and never buy or sell anything with a sticker) are somewhat stiff and flat ovals - the ball is round.
I have heard of them falling off - some suggest a hair dryer. I've never owned a stickered item. I enjoy doing the authentication myself. It is the hobby IMO - otherwise I'd be buying a list of and there would be no fun, research or learning.