This is dirt deep in the carpet "wicking" back up as its drying. Carpet was left too wet by whomever cleaned the carpet.Be observant for brown spots after it dries. We had the company that cleaned ours come out two additional times to remove the brown spots they first created.
Something about "oxidation" of the salt solution they used?
I didn't buy their story.
I've dealth with professional carpet cleaners many a time when working maintenance as they'd come in to clean carpets between rentals. First they should be pre-treating the carpet in heavily trafficked areas. Two some newer companies are using an Oxi-clean type of solution that seems to work well. Three you should have all of your furniture moved before they arrive, as some places won't move or charge extra.I'm having my carpet professionally cleaned today. I've never had someone do it for me. Are there any questions I should ask, or requests I should make? I was thinking I'd just let the guy do his thing, but maybe there's something more ...
It's either they left soap which attracts dirt over time or they got it too wet and a day or so latter it's wicking up dirt that is deep down in the carpet. They also have to use the proper cleaner. There are cleaners for organic stains and other cleaners for more grease stains. And any cleaner with something like oxyclean only works for a few hours after mixing the water with powder. Then a new batch needs to be made.If the company uses a soapy water mixture and does not go back over with clean water to rinse out the soap, the carpet will likely get dirty again rapidly