The 57-year-old victim paid €9,500 ($13,774) for a car from the Neuss dealership in May 2010. But the car salesman, apparently desperate for money, took the cash and never ordered the car.
When the victim went to pick up his purchase in January, the suspect killed him and buried his body near a motorway, the police said.
A construction worker saw a hand sticking from out of the ground and called police who discovered the body.
After some queries nearby, they realized he had an outstanding order from the car dealership, which led them to the alleged culprit.