I have never had the pleasure of holding any of the real deal figures in hand, but from what I can tell from some video reviews is this: the real Revoltech joints seems to produce that clicking noise when the joints are moved (like a ratchet) and my bootlegs' joints don't seem to make much or any noise at all. The joints on my set aren't loose persay but they are far from stiff, so I can see why they would get looser the more they are manipulated. Clearly the real figures use a better quality plastic for the joints (and more than likely every other part). I would not recommend popping the joints apart often, as the pegs seem somewhat brittle.
The joint that holds Mikey's whirling chuck effect actually broke on mine, as the peg would not slide into the spinning piece at all...so I risked it and applied a little to much pressure and ended up breaking it and oddly it actually fits better than before but is far from stable.
For the most part I'm satisfied with the bootlegs, the paint apps on mine are actually quite good but am a little upset that I wont be able to mess around with more poses in fear of wearing out the cheap joints. These could have been a great/cheap option for making some stop motion shorts but I just cant see the joints lasting long if constantly manipulated. Would be nice to find some legit revoltech replacement pegs/joints in the appropriate colors but I have yet to see any
As for a good eBay supplier, I wouldn't know as I also ordered mine from Aliexpress. Shipping was really fast and the figures arrived within a week and a half...just beware that you may get a good set or you might get a garbage one...or even a mix of both, it really appears to be a coin toss at the moment.
If you are willing to take a gamble, go for the bootlegs as they aren't all bad and at first glance look like the real deal but the quality is not going to be the same as the real ones. If I manage to find a real set for a non outrageous price you can be sure I would buy them and get rid of these.