This is a very interesting topic because it affects most of us, who chose to live different from regular 9 to 5, while chasing our dreams.
As Ope noted in his response, excellence and relationships are what would put immense value for your work, in the eyes of your clients.
While in all these, it’s also very important to properly select your client. If you ask me, I think the person you described isn’t someone you want to continue doing business with.
Something else that you can do is create packages which you sell to clients. So that whenever a client requests for your service, they know which tier they find themselves in your package. They also know what to expect as a result.
This is particularly beneficial when you just need regular money in your account for survival, and you don’t want to wait too long for that next project. I’ve been fiddling with this idea, but haven’t implemented it yet to know how effective it is.