As soon as I read "respected member of the community here since 2006", I figured it was Disciple. Michael (Disciple) had referred to himself as the previous quote, in recent months. I had also seen him and the OP get into it on another thread. I can't say it is him, for sure, that the OP was referring to, but in case it is, Michael is a good guy.
I've worked with Michael for about a year on/off with either faceplates or modules, and have never had any issues with him, nor his payments. He called attention to himself regarding a recent transaction that went south and involved a module from the OP, by responding and sticking up for himself in a public forum. The OP may not have named Michael, but he sure tried to make it easy to figure it out. Yep, classy. Maybe the OP could've used a private channel, rather than creating a potential panic within the community about an unnamed person trying to sabotage his work. But, I know firsthand that wouldn't happen.
If I was Michael, I probably would've done the same thing. By coming forward, without anything to hide and explaining what had happened.
As for any slander, If the OP has had any customers swayed to the competition, I'm sure it had nothing to do with slander.