As promised, reporting back.
We met at a neutral place, he seemed like a normal guy. We made some minor small talk and we moved onto the wheels - which are not the ones listed here but another set. I couldn't get out of him where he's sourcing these, but based on what I gather, he will have more to sell. One thing I can say is each set will be varying in condition and along with it price. Anything more than that would be pure speculation on my part and probably unfair.
The set I purchased, was not new nor claimed to be new. They were used and I knew that going in. I inspected each wheel thoroughly and I recommend you do the same. The wheels were all in good condition, no bends, in round, all stamped official Rivian part numbers. They were exactly as he described them to me in PMs and seemed to match the pictures he had sent me.
What we didn't discuss much was the tires, other than they had 2000 miles on them. The tread depth on them were (8/10-9/10) which are what I expected for an enthusiastic first 2000 miles of a heavy, fast, truck like the R1T. While there was plenty of tread, the tires however weren't in the condition that were acceptable to me, as stated in other posts I can be a bit of a tire snob. There were signs of cracking and wear that indicated one of the tires may be old or sun aged, or the car may have had alignment issues. Another seemed like it may have been driven over sharp/rough terrain or rubbed against a wheel liner. Quite frankly, I'm not sure many folks would have noticed or cared but I did. I made my concerns known and showed him what I was looking at. He didn't seem aware but also didn't give me a take it or leave it ultimatum. See was reasonable and we were able to come to a very reasonable deal.
I wouldn't hesitate to buy from him again and in fact messaged him about getting a spare wheel to the set I just purchased. As I said before each of his sales will likely be of varying condition. If you're interested in one of his listings I'd recommend you meet up with him, do your diligence and inspection to make sure it's acceptable and to your satisfaction for the price you are paying. If not, offer a new price. In my eyes, I got an awesome deal on a set of wheels and for much cheaper than I'd be able to get them from Rivian for - assuming they even had them.
Oh and in case it matters, he did show up in a R1T. Which is more than I can say while I wait for mine..