otherwise than at arm’s length if— (I) the parties are members of the same controlled group, whether or not such control is actually exercised to influence the sale price, or (II) the sale is made pursuant to special arrangements between a producer and a purchaser. (ii) Controlled groups (I) In general The term controlled group has the meaning given to such term by subsection (a) of section 1563, except that more than 50 percent shall be substituted for at least 80 percent each place it appears in such subsection. (II) Controlled groups which include nonincorporated persons Under regulations prescribed by the Secretary, principles similar to the principles of subclause (I) shall apply to a group of persons under common control where one or more of such persons is not a corporation. (d) Partial payments and installment accounts (1) Partial payments In the case of— (A) a contract for the sale of an article wherein it is provided that the price shall be paid by installments and title to the article sold does not pass until a future date notwithstanding partial payment by installments, (B) a conditional sale, or (C) a chattel mortgage arrangement wherein it is provided that the sales price shall be paid in installments, there shall be paid upon each payment with respect to the article a percentage of such payment equal to the rate of tax in effect on the date such payment is due. (2) Sales of installment accounts If installment accounts, with respect to payments on which tax is being computed as provided in paragraph (1), are sold or otherwise disposed of, then paragraph (1) shall not apply with respect to any subsequent payments on such accounts (other than subsequent payments on returned accounts with respect to which credit or refund is allowable by reason of section 6416(b)(5)), but instead— (A) there shall be paid an amount equal to the difference between— (i) the tax previously paid on the payments on such installment accounts, and (ii) the total tax which would be payable if such installment accounts had not