I have a keen eye for the types of errors that are most difficult to spot. When publishing short stories or (especially) longer works, we often can't help but rely on a spell checker, and the spell checker will faithfully flag any text strings that don't qualify as words. However, if what we typed IS a word, but just not the word we meant, we have a problem. For example, we might have typed mouth instead of month, or assent instead of ascent. These errors pass the spell check, and they have the same length (and even the right sound in the second case). We may very well miss these errors, since we don't expect them to be there after all. Errors like these always catch my eye. (In fact, the second example came to mind because this error occurred in the text of a book that I am currently reading).
I am also very sensitive to situations where a comma is required but has been omitted, or has been used where it shouldn't have been. If it doesn't sound right while I'm reading the story, I have to stop and correct the error (usually just for myself) before proceeding. Naturally, once in a great while it is I that have misread the passage, and I discover that the text as written is correct after all, but this does not seem to happen very often.
Your short story is likely 97% correct, in terms of word usage, syntax, and punctuation. I can bring that up to 99% or better.
Please contact me so that we can discuss this at greater length.