FAR more annoying to me than typos (of which I make many) are the prissy petty pedantic prescriptivists who insist on conflating orthography with grammar. Using "their" for "they're" or "its" for "it's" (or vice versa) is still just a typo. It says nothing at all about the writer's grasp of English grammar. All it does is illustrate that English orthography is a nightmare. So unless the typo has unintentionally amusing consequences, or is one of real, grossly indecent offensiveness
(e.g. spelling "espresso" with an "x"!
), I ignore them. If I buy a book and find it contains a lot of typos, I might be mildly disappointed but it would take a non-stop stream of them to really irk me.