Maryland Code, Commercial Law § 12-617

(a)(1) If a payment is made on account of an agreement, the person receiving the payment shall give the buyer on his request, or, if payment is made in cash, without request, a complete written receipt for the payment.

(2) If the buyer specifies that the payment is made on one of several obligations, the receipt shall so indicate. However, this provision does not affect the allocation of payments under an add-on contract pursuant to § 12-618 of this subtitle.

(b)(1) Unless a written notice of actual or intended assignment of an agreement is given to the buyer, he may pay or tender any amount due under the agreement or give any notice required by the agreement or this subtitle to the last known holder of the agreement.

(2) A payment, tender, or notice so given is binding on any subsequent holder or assignee as fully as if made to him.