When your customer says "I'm sure it takes little time to do it" and you know you just won another two weeks of work...

At least they’re acknowledging it will take time, even if grossly underestimating it. I had a customer send a feature request for a payment gateway I maintain for WooCommerce once that amounted to:

• Allow splitting of payment across two forms of payment
• Enable splitting the cart (or at least designating which items are on each payment method)

When I demurred by saying I’d take it into consideration if he were willing to cover the development cost (after all, both are radically out of scope for my plugin, and may already be possible with existing plugins), he insisted that the whole thing should take an afternoon at most if I just sat down and did it. That’s pretty much where it became a firm “no”.

@Kaji Another reply that has been suggested to me for cases where the customer grossly underestimates time and/or cost is letting them know that they can have it that way if they want, if they’re willing to make the appropriate sacrifices in features, testing, usability, support, etc.

"But the other dev I know says he could do it by adding a pair if-elses"
😡