Just because you work from home in your pajamas doesn't mean you can slack off on professionalism. Freelancers who are unprofessional risk losing out customers and not least damage their reputation.
There are a few things you can do to ensure you act professionally.
First, you need to be responsive to your customer. If you are not available immediately, let them know when to expect a response.
Secondly, dress the party - even if you "just" work from home, dressing for work can help you get into the right mood and mindset.
And of course, be respectful and courteous in all your interactions with your customer.