He can send you a Paypal invoice directly from the PP site.
He should note the eBay transaction number in the text box.
Then he has to manually mark the item as Paid and Sent in both the PP and eBay lists.
http://www.cbsa-asfc.gc.ca/mobile/est-cal-eng.html
There does not appear to be any difference made between new and used, for clothing or for other items.
There is a difference based on origin, so your seller will need to mark where the socks were made.