If seller provenance is that he gotthisautographfrom astudiosound engineer"Reciprocal Recording"who attendedthe recording of thealbum "BLEACH" in 1988.
Then it is not authentic. Chad Channing would have signed his full name with a z and sun below his name.
Seller might have copy these autograph from a Bleach CD that was signed at the Waterloo Records, Austin TX on 10/21/1991. That CHAD was signed by Dave Grohl. Dave Grohl was not in the band when they were recording Bleach. See the similarity!!