Get a listing of several other ones within 500 miles, rank them by mileage and year. Take the top 3 and see how they compare - I'd tell the seller that I have 2-3 others that are very similar but with different mileage. Tell them that the other sellers are very motivated and that you like the 1k car a bit more and if they could come down $X (I don't know the exact number to tell you- that will come from analysis of the other cars on the list) you would buy the car from them.

Competition between dealers is within your power. Good luck.