Sounds like a job I got tomorrow. Flat, 2nd floor, carpet is black apparently, left that way by previous tenant.
Too far to visit and quote so gave a higher than average estimate over the phone.
Never walked away to date but had a few stinkers just after starting out that I was really tempted to including a flat above a restaurant where 6 of the workers lived, hallway and stair carpets were crusted in years of black grease, health authority told the owner get them replaced or cleaned, was a bit daunting after only been going a few months.
But glad now I didn't walk, good experience and it showed me early on how a really trashed carpet can still come up well.