Alot of times, traffic area fibers are scratched so much that they hold on to alot more fine soil. As mentioned above, vaccum the head out of these areas and even utilize a pile lifter or a
CRB type machine to dig crap out first and then vaccuum. Then use a heavy duty prespray or or your general prespray and boost it with some oxygen. Let it be Hydrogern peroxide, Sodium borate ( O2), or boost with sodium percabonate (
Chemspec energizer, Masterblend accelerator), ) Let plenty of time to dwell let the oxygen get to work. Then rinse, rinse rinse. Dry and collect check.
P.S. Don't try this on Wool carpet or delicate fibers.