I bought a Ken Follet (The Pillars of the Earth ) book from WHSmiths and it had on average one misspelling a page.
These were from faulty OCR. For example, 'I'll' was always 'TH'
It was obvious that no human had read the book in e format.
I contacted the publishers (Pan Macmillan) who simply referred me to Smiths.
Smith's initial response was they had had a look at it and could not find any mistakes.
I sent an annoted list of mistakes from one chapter and they replied with thanks and a refund.
What worries me is that these books are cheap to produce, fail to meet basic quality control at times, yet still cost as much.