We sometimes like to stray away from this type of work for 2 reasons.
1.As someone mentioned earlier you have no idea what is hiding underneath that grass. Anything could be in there, like a dead cat, loppers or a log 7 inches in diameter. All of these from personal experiance. You bid a job at $40 and you ruin a set of blades, your profit is gone.
2. If I was someone driving buy and saw a yard that a lawncare company was mowing and was like "hhhhmmmmm...ok" then drive by the next day and looks like complete s&*t do you think the chances of them calling you for a service would ever happen. Not to likely. Even tho you did EVERYTHING you could to make it look good and couldn't help that the people are stupid, the driving by customer won't care in the end. The expect everything to look like a million dollars after you leave.
In my opinion people like this should pay good money in the end. If you are to lazy to get up off ur butt and mow ur yard then in the end you are going to pay me for it. I for one hate leaving a yard look like crap because that is my name on it. That is your advertising.