SAJ, I am going to put my arm chair economists hat on to answer this one...
Instead of thinking of them as customers, or potential customers, think of them as coins.
Now imagine you had a pocket to keep those coins in, all the coins were the same size but had different values, some are 5p, some are £5. Your pocket could hold 50 coins, anymore and they would just fall out of the pocket.
So, in your pocket you have 50 coins, your pocket is full. But then you spot a coin for £5 on the floor. This is much better than most of them in your pocket. But you can not fit any more in, so you have a few choices.
You can either walk past the £5 coin and carry on your merry way.
or
You can remove a 5p coin from your pocket and put the £5 one in.
or
You pay someone else to carry the £5 coin for you.
or
You put the £5 coin in and allow a random coin to fall out.
out of these I would say that, as you do not want to pay someone else to carry coins for you, you would be better off removing a 5p coin and putting the £5 one in. But the choice is yours.
If you value the 5p coin more than the £5 coin then you should start to seriously ask yourself why you are in the business of collecting coins.
likewise, in window cleaning, you should seriously ask yourself why you are turning high prices away in order to keep lower (even if they are well priced) ones. And ask yourself is your loyalty to yourself and your familly, or your customers?