That depends on why you don't like the result: If the recording contains errors (incorrect pronunciation, forgotten words or sentences), the talent must re-record free of charge, no question. The same applies if there are technical defects (hiss, background noise, room ambiance, etc.).
It becomes more difficult when subjective criteria are involved, such as artistic approach. However, thanks to online casting with auditions according to your script, such a case is rather unlikely, since you already know in advance how the talent will interpret your copy.
Important: Subsequent changes to the copy by the customer (so-called "author corrections") do not need to be recorded by the voice talent free of charge. Ideally, however, you should agree on a rate for author corrections at the beginning of the collaboration.