Sounds like it might be time to increase your rates! Increasing the average price of care in your neighbourhood is beneficial to everyone. There is a difference between undercutting your competitors and being competitive. We work very hard, deal with a high stress level and have high liability for very little pay - if you feel you are undercharging than by all means raise your rates!
To provide care without receipts is illegal. My business is legitimate in every way and that includes giving receipts and claiming my income.
Good luck!