One guy dealing himself quads twice and a straight flush once in a few hours is suspicious but doesn't prove anything.
This makes sense, but suppose you spot something. Now what do you do? You still can't prove it. It's just an ephemeral moment that you can't, say, show to the host to ensure the cheat gets 86ed. Even if you grab the deck in his hand mid-cheat à la "I caught a hanger, Sarge," life isn't a movie. You're not going to convince people he's cheating because the

was at the bottom of the deck.
If you play with him again, surreptitiously record him while he's dealing, e.g., by propping up a phone to aim at him or wearing a hidden camera. If there are any more unusually big hands or coolers that stack other players in his favor, watch the video. Pay attention to how he collects the cards from the previous hand. Pay attention to how he shuffles, cuts, and deals. Compare his procedures and body language to other hands where nothing special happened for him.
I caught a cheat years ago and didn't do this, and it of course made my case harder. I'd been in communication with the host, and apparently I was convincing enough to get the cheat out of the game, but it's hard to expect people to take your word on such a severe accusation. Proof is better.
Also, be a dedicated dealer or be a dedicated player. No one should be playing
and dealing for everyone. Nine times out of ten it'll be fine, but the tenth time you'll have a practiced cheat offering to deal
every single hand, and that's obviously a disaster.