This has nothing to do with default seller settings for combined shipping. I bolded this because I know that's the first kneejerk response all the "helpers" here will start blindly typing. eBay recently changed Best Offer purchases to automatically process sales the moment sellers click on "Accept Offer." If buyers make multiple offers on a particular seller's items, buyers have no way to request a new total, as each offer is treated as an individual transaction. Many sellers who advertise combined shipping in their listings are failing to do so as a result, either out of ignorance or malice.
Some sellers are simply refunding the difference between charged shipping and actual shipping (and that's fine, but just more work for sellers to do after the point of sale). However, some sellers are flat-out refusing to recredit erroneous shipping costs despite their advertised combined shipping policies. As usual, eBay will not step in and enforce their own protection policies (after all, why should they? That's just more Final Value Fee revenue for them). If buyers have already received and opened purchases before they realize they paid more than double what they should have been charged for shipping, and sellers are unwilling to honor their own combined shipping policy, buyers have no recourse other than to leave negative feedback.
I don't expect this to be addressed (much less fixed) by eBay any time soon. The Combined Shipping functionality has always been very poor on this platform. However, this issue has only surfaced since accepted Best Offers were changed to automatic payments.
