I don't see where you set the MTU/MSS? Are you sure you have set them somewhere else? eBay is known to have problems with bad/wrong MTU/MSS. Try adding scrub out on $ext_if max-mss 1414 to your pf.conf and adding -mtu 1454 to the route. Also take a look at pppoe(4) [*NOT* pppoe(8)!], section MTU/MSS ISSUES.
-- Jonathan
