If you get mud, tar, grease or any other hard to remove soil on the carpets try Tuff Stuff (you can get about anywhere).
Spray the area and let it sit a few minutes, then use a damp rag to work the area and a then continue working until the stain is removed. Most stains are removed very easily with this product.
This product will work on any surface that needs cleaning. If you use to clean leather seats and such they then need treated with a conditioner.
Tuff Stuff is the best product I have ever used for cleaning carpets in a vehicle.I cleaned a well used truck a few years ago, it had light gray carpet that was stained with grease, tar, and general grime. After using Tuff Stuff they looked brand new.