How do you know if they've paid their bills? And does that really matter? It's not like you'd arrive to the home of a frequent flyer and say "Sorry man, you're delinquent in your bills. Wish I could help you, but you know. Rules."
I don't handle billing, and I'm really not sure why that would have any effect on field treatments, regardless.
I do know, that per policy, all treatments are billable - but in practice some are not processed, for whatever reason.