There a million and one regs having to do with anti-kickback, stark, etc.. not sure which if any apply. What I referenced was a form of kickback IF The billing company taking the referal gives you a fee based on revenue in any way. I personally don't charge or pay referral fees as it's part of networking. I've given clients and I've received them, to me that's cost of business and networking. If a fee is to be arranged, to be safe, I would go a flat rate, a gift of some sort but would NOT do anything in regards to the practice receivables.