So you would overcharge the person with a relatively easy clean that takes half the time and feel happy about that?
No, i would feel happy that i have given the 'relatively easy' clean an honest, high quality clean that she is entirely happy with and one that i feel i have given my all at. what is wrong with that :
, as for the harder one - i would feel, hey ho, its a toughy but im prepared to do it nethertheless.
This scenario wouldnt work if your working to budget cleaning, as you would feel peeved at working so hard for so little :
Dont forget, the person you gave a lower price to, will expect this lower price next time (even if its on a dirtier carpet), and will tell all her friends the price too. then when you go and quote, you have to try and explain to them 'why' its gonna be more. they will smell a rat - even though there isnt one.
Mark.
p.s. jim, same as me then on pricing 
Mark I'm with you on this one.
Mike I think Mark and i will have to agree that we prefer another way of doing things which is equally valid as your way.
I would just point out that in some way you will almost certainly be charging more even to the easy clean to reflect the time undertaken to do the quote although i appreciate that will also be reflected in the difficult one as well. I presume Mark and I if we are quoting over the phone will save both examples something on the overall bill because of this.
There are many examples where we take the rough and smooth for granted. Insurance premiums is one in that we all share in the overall costs of running the insurance company and although premiums will be different to reflect different circumstances there will still be an element of averaging about them, especially if you never claim then you will feel as if you are being ripped off.
A second example if you want to buy something, you research what you want and where you are going to buy it from. You buy it and are happy with the purchase. A week later the shop is now selling that very same thing at a cheaper price. Was the shopkeeper ripping you off? No he's just taken a hit on his margins instead.
So Mark and I are charging correctly for the easy clean but taking a hit on the difficult one. Those difficult ones are thankfully few and far between and so as Mark says "hey ho".
Dave, to answer your question and assuming everything about it was average and relatively straight forward then I would be looking for probably £60+vat.