I have actually gone behind a few people in this area and left a big clean square usually in the dumpster area.. It is usually funny to go back out the next day and if your lucky you will see the little guy with the cold water machine back out there recleaning the concrete ,, While I am not one to take away those $30.00 concrete cleaning jobs, heck I don't even like to clean concrete.. But I feel it is my civil duty to inform a customer when they are being taken advantage of... I usually tell them if they don't want to pay to have it done right that could get the same results with purple power degreaser and a hot water garden hose...