Be confident. We send a formal estimate with before pics of the project using joist. Check out joistapp.com. I snap pics and type up the estimate with my phone and send it to them within minutes of us meeting. When the job is over you don't have to be shy about asking for payment. You've already set expectations and customers expect to pay when the job is finished.
If you need an icebreaker, after the walkthrough, ask if they're happy with the work. Once you get confirmation ask should I run to the truck to get the credit card swiper or will you be paying with a check or cash.
You did the work. The customers expect to pay. They're happy. You've earned it.