I have read the claims concerning 303 Fabric Guard as well. Here is my take on it. I applied the 303 to my new 2002 Ford f-150. I will probably shampoo the carpets once per year. I only plan a once per year shampoo because I vaccum the front mats and seats off after each drive(takes about 3 minutes or so to do this). Wife says I am crazy. but here is my logic. I find that by vaccuming after each drive, I avoid build up of dirt on the mats and seats. This prevents the "super cleaning" that would otherwise occur. The back seats, matts etc are vaccumed weekly.
I think once you shampoo the car upholstery, you should re-coat with the 303 Fabric Guard. I plan to shampoo my mustang's upholstery in about a week. I will use a Bissel Little Green to extract the soap and water when I am done scrubbing.
I figure that using an extractor, you are also extracting all of the fabric guard you have applied to the material. I also say that friction of feet, dirt etc can wear away the Fabric Guard.
I say vaccum, shampoo, then reapply the 303 Fabric Guard. My 2 cents.
SJ