There are various ways around this.
(1) When you quote, charge more for the first clean - but don't tell them. If it's accepted you have a well-priced job. If they try to knock it down, agree but say you do need to charge the amount you quoted for the first clean as it takes longer.
or
(2) Decline then politely explain that if you worked at their suggested price you would need to work too fast to give a quality job. Also, that after a while you would find working for their price irritating and you prefer to be happy in your work.
or
(3) Before walking away explain to them that when someone haggles the price, it makes it difficult for you to increase the price in the future. Therefore, you would prefer to avoid such a situation by not proceeding.
I've done variations of all three. Keep it polite and professional. You might not gain a customer, but you've kept your dignity and maybe even helped someone to review their attitude towards tradespeople.