Agreed. I'd rather take a beating at the local shop for trade in than deal with those folks.Meh. It’s not like it’s a proprietary supply. It’s a readily available 9V DC 500ma adapter. He bought a used pedal that wasn’t advertised as having a power supply - wasn’t advertised at all.
Heck, a “brand name” supply is well under $10. The guy is a freak and a bully.
If it was an odd voltage, or something proprietary, I could see a follow up from the buyer to see if the seller forgot to include it, but I don’t think I’d be bothered to do that in this case.
IMHO this falls into the category of folks who shouldn’t buy used...in the same league as expecting an original box, hang tags, a COA, a generic truss rod tool, no Velcro on the bottom of a pedal, or the inclusion any other inconsequential case candy. Stuff that only has any real value because a few folks on the Internet have given it value.