On average, there are fifteen spelling or grammatical mistakes, typos or formatting quirks per published book. To get to this average we include some self-published books that are dire, some absolutely perfect ones (rare) and the vast majority that have between five and twenty such problems.
Can we improve this? And how do we get to even this level of what is, after all, mainly correctness? There is more right than wrong and we want to keep it that way.