With years of experience in illustration I know that today buyers love to have vector source file for their projects. So I've just submitted a pack of additional files.
Before I'm used to add an ai vector additional file to my illustrations.
Now I've experienced that eps file saved as an AI8-compatible EPS is more editable and easier to use by buyers that can open them with both Adobe Illustrator and Corel Draw. So I'm saving all in EPS, will buyers thank? I really hope so! :)