editing - How many errors should I expect from a proofreader?

I hired a proofreader (typos, commonly confused words, minor grammar issues etc) to look at my work, which I plan to self publish.

She found most typos, but from a 66,000 word novel, missed about 10. Things like using 'its' instead of 'it's', 'you' for 'your' etc. I found these on my own last read.

Now I realise nobody is perfect, but if I'm hiring a professional proofreader, how many errors are acceptable?

Answer

Ten out of 66,000 words would be acceptable to me, particularly if the proofreader has only gone through it once. You always catch more on the second round because on the first you're reading for both structure and sense, and the second time is primarily for structure.