A professional or business site is one where the primary purpose of the site is to facilitate business transactions. You can sell items directly online or exclusively offline, but the result is the same. You want customers to buy products and/or service directly from you.
To create a domain name for this type of website here are a few guidelines:
1. Shorter is better
2. Make the name easy to pronounce
3. Think long term
4. Stick to Categories and Topics
5. Do a trademark search
6. Always have a tag line
