Cleaning Restaurants means dealing with a combination of issues. There's grease from the kitchen (protein) and heavy oils from the parking lot (petroleum). There will also be many drink spills that may re-soil rapidly because of the sugars in the drinks attracting soil.
For a pre-spray I highly recommend Pro-Zyme for those of you who like powders and Dirt Chaser for those of you who like liquids. As a side note any of these enzyme based pre-sprays can be used as protein spotters. If grease and oil from the parking lot (petroleum based) is an issue around the entrance any of these products can be boosted with Energy.
If the area is heavily soiled Extreme Clean will be the most effective for cleaning and establishing a positive environment for continued carpet maintenance. Once an effective maintenance program has been put into place SCR (Soil Crystallizing Rinse) can be used to effectively clean and maintain the area.
Drink spills from soda, beer, and mixed drinks will contain sugars that while they appear easy to clean initially may appear to come back. This rapid re-soil situation can be corrected with ARA (Anti Re-Soiling Agent). ARA contains polymers that will encapsulate and crystallize any sticky residues that can attract soil.