If it was sold by a business then usual trading laws apply.
This link might help.
If someone has a trading record on eBay (or anywhere else) then they are selling in a business capacity even if they present themselves as a private seller. It's worth looking at his completed listings and current items to see if his activity constitutes trade.
Does his 7 day period refer to a refund if you just don't like it or a refund if it's not working?