Officers have impounded an Audi TT and are investigating whether the car is linked to a nationwide cloning operation.
Owner Robert Wyper, who began the business in 1999 and also operates a Renault approved repairer franchise, insists he is innocent and bought the car from another dealer in good faith.
Police are tracing a nationwide scam involving up to 150 stolen cars which have been given the same registration plate as legitimate vehicles, known as cloning.
He told Scotland's Sunday Mail newspaper: "They were interested in an Audi TT which I bought in good faith from a dealer in Leicester.
"I paid £20,000 for it and sold it to a customer in June. The police took away the paperwork in relation to that car and have recovered the Audi."
He has provided a replacement car for the customer, and said the business would take the £20,000 loss.
Wyper said officers told him two other motor retailers have been conned in the same way.
Wyper headed franchised dealer group Robert Wyper Motors until 1998 when he sold the group to Parks of Hamilton.