I rented a Ford Fiesta from Alamo Car Rentals at Gare du Nord, Paris, for my tour through Northern Europe (specifically parts of France, Belgium, and Germany).
The first problem I had was finding the car.
In the station, I followed the signs for the taxi rank, which was out to the right-hand side of the station as I arrived, just near platform three. Just before I left the station for the taxi rank, I saw a set of stairs on the left going down to the basement area (level -1), where I found the car rentals. I only saw one or two signs directing me towards car rentals in the central station area, and the location shown on Google Maps for the rental counters was wrong.