In a world where competition can be thick you don't want to stand out in an unprofessional way by not being certified when your competition is. Customers will automatically brush you aside as a newbie and not want to trust you with their pets. But just by getting any certifications that apply to your business, can give you credibility that you didn't have just yesterday.
For pet sitters there is Pet Sitters International an organization dedicated to the promotion and professionalism of pet sitters everywhere. Membership is affordable and you can proudly display their logo on marketing items and on your website.
There's also the National Association of Professional Pet Sitters, and their goal is to give support and foster success to all pet sitters. Both organizations are a good start to launching and continuing on the right path for your pet sitting business.
Also if in your community you need a business license to operate a good place to start is at your city treasurer office. They can either point you in the right direction or see to it that you get the right business license for your operation.
You need to remember that in addition to launching your pet business and all the 'fun' stuff, there is also administrative needs that have to be looked at in order to keep your business professional and profitable.
Look around your community and if you have competition find out all you can about them. What certifications do they possess, how long they've been in business and look for loopholes in what they provide and see if there is room where you can do it better, more efficiently and/or smarter.
Starting your business is exciting but just remember that it is a business and should be treated as such. ~Best of Luck
