I would say that any client that is soliciting a tech to do side work is looking for a deal. They want to take advantage of the tech's skills, talents that were paid for by formal training in on the job training, things that cost the installing company money. That, by definition, is edging toward unethical. And I'm sure that most clients really wouldn't think of it as really unethical, but at the same time would never ask me if it was OK to hire my guys on the side. Human nature, I guess.