We a very diluted water based dressing. We cut ours 70% water, 30% concentrated dressing. Like Ron said, spray it on, wait, the buff it off. We are very diligent when it come to the last step. The last thing you want to see is your customer slip when entering the vehicle due to slick floor mats.
Somebody (apparently from WeatherTech, given that his user-name is Weathertech Guy) just posted something yesterday about products they sell for treating their plastic/rubber floormats. Their site is something simple like weathertech.com or somesuch.
The folks at our local (BMW) dealership gave me a bottle of some no-name substance that they use for the mats on all their newly delivered cars. I liked the sheen/non-slip properties so much that I asked for a sample. The detail "boy" (looked no older than 15 years old) told me that the shop buys it in bulk and that the only name on the drum is "Optimal" or something similar. Any clues as to who makes this product?
I'd love to get my hands on somemore without going back to the dealer with cup in hand (pun intended), and this may help the OP too...