I charge a $65 minimum, that gets them 1 hour of gutter cleaning then $50 an hour after that. The reason I don't charge per linear foot is this: I have done two identical homes, side by side with the same exposure to the same tree line. On one of the homes, the owner had them cleaned yearly and was bugging the GC during the construction of his 4000 sq. ft. home. The other guy bought his home when it was over two years old, and had no idea if the gutters had been cleaned or not. The first guys gutters took one hour to clean and none of the downspouts were plugged up. The second guys gutters (on a virtually identical house) took three hours to clean including some minor repairs and half the downspouts were clogged. If I had charged per linear foot I would have over-charged the first guy and lost my shirt on the second guys place. I will give rough estimates for gutter cleaning, but there are too many unseeable variables (neglect, plugged downspouts, #@*! gutter guards) for me to feel comfortable charging a flat rate.