After you have laid out all the details and specifics with the photographer, it is an absolute necessity that you get everything in writing to ensure you are satisfied in the end and have legal recourse in case you don’t get what was agreed to. Also, if the studio says that they have the right to send any staff photographer they have available and if you are not comfortable with not knowing who will arrive, then you should not sign. Or, if you have talked to most of the photographers and you feel uneasy about just one of them, you still should not sign with that studio because you will inevitably get the one you do not feel comfortable with.
It is important you have built a rapport with the photographer, know his work and feel secure that he will do the job you want because you do not want to be worrying about him or her on your big day because there is already enough to do. Only sign a contract for the individual you want and never leave your pictures up to chance because these photos will be your way of reliving your wedding day.