When i started out i had a pricing scale,which went up according too the amount of crud ! The thing is with the real mingers,they are usually really cheap carpet,so you have to find a balance between cost of cleaning and cost of replacement.
I now charge more or less the same,just got back from doing a 1950s semi 3 bed 700 sq foot,booked me yesterday,as other person let him down,now i said wrough idea of price over phone,got there measured up was £214,said i would be happy with £180,job took 2 hours so i was also happy,he was not expecting miracles,but i got them cleaner than he expected,now i could have been a sly beggar and charged him more,as he was stuck,new people move in on Monday,but i would rather him be happy with price,so he will more than likely use me again ,and tell his friends.
Just my 2p worth