...but yes I agree with you.
Many years ago I saw an advert from a company who sold word processing software and their advert had a typo on roughly every third line !
I replied to them in kind, asking why they didn't run their advert through their own Spell Checker !
Also I have noticed that the cheaper eBooks appear to have been proof read by people whose first language is not english, and learnt the language by listening rather than writing it.
e.g. "given" instead of "giving"........"wages" instead of "wagers" (that was on 2 consecutive lines so not a typo)
...and I plead old age and poor eyesight for my own tipos...