You're assuming his use of copyrighted and trademarked material is authorized.
They're selling books and even soaps with "deadwood" in the name, and they / the publisher (sounds like they're both run by him?) appear to have directly lifted the photo for the cover of one of the books:
My guess is that Seitz got nailed by trademark and copyright infringement claims and is now spinning a story about how his poor poor book shop is getting screwed over by the Big Evil Corporation, as witnessed by the very histrionic language he uses in his tweets.
Trademark cannot stop someone from using that word on an unrelated product like soap. Nor can it stop someone from using a word in a book title.. Is Amazon killing the book industry? is a valid book title.
I'm not a lawyer, but "Deadwood Soap with a Prize Inside: Dirt" sounds like it could suggest sponsorship or endorsement to me.
Of course, as teh_klev pointed out, this most likely isn't the cause of the store's Shopify problems since HBO says they're OK with what the store does.
They're selling books and even soaps with "deadwood" in the name, and they / the publisher (sounds like they're both run by him?) appear to have directly lifted the photo for the cover of one of the books:
https://mzs.press/The-Last-Western-Deadwood-and-the-End-of-A...
...from here: https://deadwood.fandom.com/wiki/Deadwood_(episode)?file=Sea...
My guess is that Seitz got nailed by trademark and copyright infringement claims and is now spinning a story about how his poor poor book shop is getting screwed over by the Big Evil Corporation, as witnessed by the very histrionic language he uses in his tweets.