"If you ask him, he will refuse."
Translation:Se vi petas lin, li rifuzos.
Because the English doesn't have a hypothetical -- it's a certainty (what some sites call "first conditional").
Hypotheticals (and in Esperanto, the -us ending) are the domain of second and third conditional ("If you asked him, he would refuse" and "If you had asked him, he would have refused" -- both "Se vi petus lin, li rifuzus").
But the meaning is definitely hypothetical. If you weren't trying to do a word-for-word translation, would it make sense in Esperanto not to use the conditional?
I do not see it as hypothetical at all -- on the contrary, it is a surety: If you ask him, he will definitely refuse.
Just like: If you heat water to 100 °C/212 °F, it will boil.