In reality this isn't a difficult customer. This is a customer. The issue arise from the fact that neither you nor he was clear about the scope going in.

He provided a form to quote and you did it. I imagine that the form was fairly vague and didn't addresses scope changes, final acceptance, review cycles, cost for changes, etc.

So the first thing for going forward is DON'T DO ANYTHING MORE unless the process is spelled out and agreed to.

As for the current situation - your prices vs others. That's easy. Compare quotes and show that the quote he's using for comparison doesn't include the changes you made. So the initial cost was probably equivalent. But changes cost. When he balks at the change costs, walk him through what he asked for, what he changed, and what it took to implement those changes.

This will also be helpful in going forward. It will show him the importance of being clear up front, and that changes need to be assessed and agreed to before just being requested.

In reality this isn't a difficult customer. This is a customer. The issues arise from the fact that neither you nor he was clear about the scope going in.

He provided a form to quote and you did it. I imagine that the form was fairly vague and didn't address scope changes, final acceptance, review cycles, cost for changes, etc.

So the first thing for going forward is DON'T DO ANYTHING MORE unless the process is spelled out and agreed to.

As for the current situation - your prices vs others. That's easy. Compare quotes and show that the quote he's using for comparison doesn't include the changes you've made. So the initial cost was probably equivalent. But changes cost. When he balks at the change costs, walk him through what he asked for, what he changed, and what it took to implement those changes.

This will also be helpful in going forward. It will show him the importance of being clear up front, and that changes need to be assessed and agreed to before just being requested.