At this time, Zentail does not support auction listings on eBay, or 'Make Offer' or 'Best Offer' functionality on listings on eBay. 

While listings with Best Offer as a purchasing option can still exist while using Zentail, Zentail recommends converting these product listings into normal listings without any Best Offer functionality.  This must be done in your eBay product dashboard.

In the future, Zentail aims to offer more features built around auction handling and Best Offer listings.