You are in luck!
There is a thing called "user" that is very helpful in these circumstances. It has amazing pattern recognition and ability to distinguish whether a string of characters is the name of an author, a book title or something else. And the "user" can even fix problems! Usually you find the "user" mounted on the chair in front of your computer.
There are some plugin that can be helpful and let the "user" work slightly more efficient.
Quality check.
Find duplicates.
Extract ISBN.
Extract ISBN is interesting. I haven't tried it, but I assume that you can let it find ISBN and after that easily download metadata for that exact book, no guessing involved.