(a) A retail seller may not induce a person or a husband and wife to become obligated at substantially the same time under more than one retail installment contract with the same seller for the deliberate purpose of obtaining a greater amount of time price differential than is permitted under this chapter for one retail installment contract.
(b) A contract made by a retail buyer and retail seller after the 30th day after the date of a contract between that buyer and seller is presumed not to violate this section.