Take Clayton's description of the guy to the other music stores, particularly the Make and gauge of the strings he bought, if Clayton can remember. Or the way he selected strings - or did he mention they were for a specific guitar? When I worked in a music shop we'd get people who were memorable for their preferences - you didn't refer to them as "the tall guy with the glasses", you said things like "Mr two packs of La Bella silk and steels and a pack of extra slinkies".