In that case, forget about it. He might not even have a username or ever post on the forum. It's not like these messages are private. It becomes his problem in the future since he doesn't have feedback if he wants to buy/sell and the next guy won't deal w/ him w/o previous references.
If you think he does have a username, do a search on google or yahoo by typing his email followed by site: tt.tennis-warehouse.com to find threads where he might've posted his email before. You could also try w/ his name. The key is the site: search.
Back to using POGs. Why did I ever leave you dear friend?