How, oh how do you

How, oh how do you convince someone not to do something?
person: do you have a large version of that image that I can blow up to the size of a house?
me: no, we didn’t purchase a large size. The one we did purchase should not be blown up bigger than 14×20 at 110dpi. If it needs to be bigger, we need to buy a larger image.
==day later==
[comp received image is indeed as big as a house, is not the larger one, is distorted and blurry]
me: This will not print well.
person: why?
me: you blew up the small image, there are not enough pixels there to make this look acceptable to the human eye.
person: what?
me: you can’t do, what you did to the image.
person: why?
me: [strangling phone] it won’t print correctly
person: it prints ok here

[I tap out]