I have an outstanding medical bill for a careflight service provided for my son in an emergent situation. I live in TX and service was provided in TX by a Missouri company. Insurance paid a portion of billed charges and the balance has fallen on me. If I send a check to them for an amount less than the bill with "for full and final settlement" in the memo and they cash it, is it binding?
Generally no. What you are talking about is called a "restrictive endorsement." The current version of the Uniform Commercial Code (UCC) essentially says that language written on a check does not alter an underlying obligation. For example, if the debtor owes $X, and sends a check paying $Y (which is a lessor amount) with a comment in the memo section saying something to the effect of cashing this check shall be deemed payment in full, that language is not binding. However, the UCC can vary from state to state.