A professional is suppose to treat their clients with respect, do the job to expectations or better. Produce above average images consistently, deliver the final work on time or sooner. Be flexible during shoots, if something happens that requires a shooting change, don't whine about it. Once you accept a contract from a client, they have the rights to ask you to make changes, within reason, and if you are experienced and skilled enough, what they ask for should not be an issue.
I tell all my clients that I am the easy part of the event, just give me a shot list of what they require, and let me go work. There are other things going on that will require more attention, worrying about the photographer they hire should never be a concern.