There are a few ways to set members in a particular usergroup apart.
You can you the usergroup HTML markup (for their user name), use Rank images, and customize the titles. I like using rank images assigned to a usergroup myself.
How many "Vendor" users do you have or expect to have? You could just customize their title individually from the Admin CP if its not many.
User Titles/User Tile manager in the Admin CP are only set by post count.
You can just mark it up in their usergroup.
User Title
(Use this to override the default 'ladder' of user titles)
Code:
<span style="color: #000000; font-weight: bold; font-size: 12px;">Vendor</span>
Change to whatever color and size you want.