I also did a one off clean yesterday on a three storey house with seven windows cleaned inside and outside and she never moaned at my price at all.
But like spe said money is money no matter if it is a one off or regular and i also find the one offs do pass your number on more regular than a regular client do. And I have wonder why it is??
But so of my one offs have become regular clients they phone me when they need it doing and they are in places where i clean regularly.