You could just ask him if he wants a cell phone video taken to see how low he goes.Some guy was squatting next to me yesterday and was telling me he wanted to hit clean reps at parallel or just below. Guy kept getting people to spot him for singles and asked them every time if he hit parallel. They kept telling him he was, but breh every single time he wasn't even close. Eventually failed on 365.
I know not to give unsolicited advice on form in the gym or else they get all, but man it was kinda hard to hold it in and not say anything.
On another forum, this dude was all proud that he could squat 400+ pounds, but his leg press was in the 300+ lbs.
I told him that you can usually do more in the leg press because your body is involving less of the lower back. I told him he's probably not going down low enough in the squat, I didn't call him a liar or a p*ssy because he was a relatively cool dude. He didn't think so. So I suggested that he get a cell phone video of himself doing a squat with heavy weight. He thought that was a good idea. He never replied about that video or his squat capabilities after that.I took a video of myself once just to make sure how low I'm going. Not ATG but about parallel.
I'm back from an injury. 
