I could use whatever payment method I wanted with my therapist - it was a larger practice so they probably just built fees into the business system of the practice. Whatever the case, the secretary handled the payments and I always was given a receipt when I paid. I would expect a receipt from a therapist, particularly if I paid in cash so there was a paper trail of payment. With a check, the canceled check works as documentation and billing statements work for credit and debit transactions. But be sure to get a receipt for cash payments.