It happened overnight at Nimey's New Generation Cars in Utica.
In a Facebook post, the dealership said the door was taken from a 2018 Honda Accord.
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They said that they would like the find the door and thief, adding: "We're offering a $1000 reward to anyone who has information that leads us to the door and the culprit."
An insurance industry source tells FOX5NY.com that a used replacement door would cost about $1,500 plus labor and paint costs.
The dealership said it would be reviewing footage from video cameras to see if they can spot the thief.
The dealership markets itself as the Mohawk Valley's largest independent used car dealership.
(Nimey's New Generation Cars)