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I would worry less about what your communication to them says and more about identifying the market. To get a 20-40% return on who you contact, you're going to have to put in some major work into who these site owners are and if they want or need help. This isn't a numbers game, it's a market identification game. If it were me, I'd spend time on a few web design and website development forums looking for people who are asking questions about their site or have concerns, and then develop conversations with them. Step away from this being about you and make it about them. Hope that helps!