From an ethics perspective, I look at it like this. As long as I'm not intending to build a legitimate business off of someone else's hard work, I think it's okay. I've sold a handful of pedals since I started building, all of which were priced just to break myself even on my costs. Mostly, the person's desire was for custom artwork or a handmade feel. Otherwise, if I make stuff just to experiment and then it sits around, I'll just give it away to friends. If a company came to me and asked me not to build something, I wouldn't. But if that same company sells "their version" of a Tube Screamer, or a Fuzz Face, or whatever, I probably would let them know how I feel about their hypocrisy.