I read through all of this too. It just seems that 1. why would the consignor decline? 2. if he did decline, especially "in writing", then why not post proof?

As you suggest, maybe the reason is more complicated, e.g. some was sold, consignor not happy to have what's left returned and no compensation for what was sold, so refused to just have the smaller amount of stuff returned. If so that could have been much more clearly expressed in this letter. And again they could just post the correspondance.