Don't think this quite beats Kinver, but...
less than 10p size , wax black boot polish on 80:20 green carpet.
Discuss 1 minute, apply citrus gel, 10 seconds. Spot gone.
flush out with spotting machine (partly to make job seem longer). 2 minutes including getting it out of ambulance
Paid £24 (my then present minimum charge) plus £1 tip.
Was working in next door property when my ambulance was spotted on next door's drive.
Justification given by husband for paying this money" the carpet is 1 week old. My wife told me not to clean my shoes in the bedrom with the barnd new carpet. If you can get me out of the dog-house then this is money well spent."
Year 1999 prices apply to example. Works out at about £500 per hour.
Rog