I think it's all about 2 words: Flexibility and Adaptability. If you are flexible in your outlook and can adapt to different situations you can cover all bases without losing out through lost potential customers. Some people may be willing to pay £95 to have their bathroom carpet cleaned, but I would imagine the "Pareto Principle" ( 80-20 ) rule would cover this situation with 20% going for it and 80% not going for it.
If you do not get in, you have no chance to impress, no chance to develop a long term and profitable relationship with your new customer. Plus the recommendations that would follow. Anyhow!! in my case, mimimum charges come into play in only about1 in 10 enquiries.
Perhaps we should ask ourselves: If we were not carpet cleaners, how much would we be willing to pay for a callout?