Bought an old Sony big red amp from him. Packaged well a delivered in a timely manner. I benched tested it and it didn't work. He didn't act like it was my fault and was willing to work it out. Then I remembered that you had to have power hooked for a minute before connecting the remote wire with these amps. Some kinda protection feature. Did that and it worked perfectly.
Just because I have 2000+ posts doesn't mean I have learned anything.
A bit delayed - thanks for the feedback. My reputation as a seller is more important than the small sum of money I'd be out. I know there are others here who do business the same way. Thanks to Jeremy for also keeping a level head and figuring out what the problem was.