It sounds like you're talking to the wrong "potential" clients. You don't "ask" for your hourly rate, you tell them. I've found the best way to get new clients is through networking and referrals. It requires the ability to sell yourself but if you lack that skill it's something you can learn.

I recommend Brennan Dunn's book Double Your Freelance Rate. It's not as much about your development skills (but you should have those down too) as your ability to manage the project, meet expectations, and relate to the client.

With dev vs plumber, do whichever you most enjoy.