Curious -- We do have the "Best Offer" feature available on our lister page. The feature only shows up in certain conditions though that match the requirements set by eBay.
The first requirement is that your item must be listed as a "Fixed Price" listing.
Secondly, you will need to select a category.
Once you have selected a category, you will now have a checkbox below the price fields for "Accept offers from buyers". Choose this to view the fields needed to use eBay's Best Offer feature.
-Kevin