Mass. Gen. Laws ch. 106, § 9-207
(b) Expenses, risks, duties, and rights when secured party in possession. Except as otherwise provided in subsection (d), if a secured party has possession of collateral:
(4) the secured party may use or operate the collateral:
(c) Duties and rights when secured party in possession or control. Except as otherwise provided in subsection (d), a secured party having possession of collateral or control of collateral under Section 9–104, 9–105, 9–106, 9–107 or 7–106:
(d) Buyer of certain rights to payment. If the secured party is a buyer of accounts, chattel paper, payment intangibles, or promissory notes or a consignor:
(1) subsection (a) shall not apply unless the secured party is entitled under an agreement: