I have no direct experience, but can throw in a couple things you may find insightful.
He is in New York and I do not believe he can hold the items he is listing locally. If that is true, he is brokering for others. (Nothing wrong with that. Just pointing it out.)
I have noticed that the ads/pics in some cases are copies of items held at other online dealers. Again, he may be brokering for those dealers.
From what I understand, he has a long established reputation in the community and I have never heard anything bad. Some have billed him as the "Go To Guy" for odd stuff you might need. My personal feeling is that I would rather deal with the real owner of an item, if that ownership can be established. Before anyone gets snarky, I am talking about items that the real owner is actively selling on their own that are cross-referenced on his site. Interfering with what might be an exclusive arrangement in other circumstances would not be ethical.