Proper way to Clean Carpet

From time to time new carpet cleaning companies advertise things like,

"We do not leave a shampoo residue in your carpet!" or

"We use only mythical water on your carpet, so no residue!" or similar claims. These gimmicks use a half-truth to try to get your business. They are correct that detergent residues in a carpet can cause dirt to bind to carpet fibers and resist removal by vacuuming. However, the other half of the truth is important.