Q about billing Personal Injury Massage

Hi all, first time poster here, first time to the site. I have a few questions that I need answers to.

First off, I practice in Maryland. A little background, my boyfriend's sister recent got in a car accident and asked if I could massage her. From my limited understanding of massage billing, if it's Workman's Comp or PIP claim that chances of getting reimbursed is very good.

It's been a looong time since I have done any really research into insurance billing. I will be doing some research this evening, but I have some questions:

1) What is the greatest pitfall in billing insurance?

2) Before you start treatment should you get a letter of intent to pay from the insurance company, rather than call and just take the verbal approval? (Is that even possible?)

I'm really in the dark about this one, so any helpful information is GREATLY appreciated!

Thanks!

Joyce