I had a conversation with a colleague the other day about how we present ourselves. We agreed that you should always be at your best. Why? Because you never know when you are going to interact with that person again.
Consider the salesperson who makes a call on a prospect. And consider that this salesperson does not succeed at securing the business. Down the road, this same salesperson is now with a different company or is a small business owner and runs into that same prospect. The prospect is going to remember their experience with the salesperson.
People always remember their first impression of someone - especially when the run into the again in the future. So, don't burn any bridges and always be on your best behavior. Do a gut check before you walk in the door. If you can't be your best, reschedule.
And, just for grins - if you find yourself rescheduling a lot of appointments, it may be time to reconsider whether you are in the right position. Set yourself up for success - every time.