Hi @keithcclark71,
Based on experience, most likely your ebay.com is never just that. It always contain bunch of connected URLs embedded, which you can easily prove with simple pcap. As you already stated, it is most certainly tied with your blocking options.
I'm not aware of any other option apart from analyzing what portals it is polling and permitting those too (which is most likell very dymanic category).
BR,
Milos