UPDATE 9/16/21 @ 10:20 AM EST: The percentage differential between the two lowest cost Ebay coin dealers selling in quantities of more than 10 has jumped to almost 3%. It hasn’t been this high since early February 2021. This could signal some stress in the Physical Gold Market (assuming that the differential remains elevated).
As you can see in the above graph, this differential has remained subdued for over a month. The last big spike was on 9/8/21 when it hit 1.98%.