When buying our 5er I went to one dealer who had exactly what we wanted. A new unit. He quoted $40k (rounded off). But it had a lot of rust on the undercarriage. Went to another dealer who had a unit exactly like the other dealer, also new. He quoted $41.5k (again rounded). I told him he was too high, I had found the same unit for $40k. He said, ok in that case my price is $39k. Shows how they can juggle numbers.
Find the lowest price among all the dealers and use that to negotiate with your preferred dealer.