Hehe gotcha - love Tour Bite, son uses Revolution, but I've yet to try Barb Wire.
Anyway, the strings that seem to get the most demand in my area are:
Mantis Power Synthetic
Gosen OG-Sheep Micro
Mantis Comfort Synthetic (has a very comfortable feel...but probably pretty stiff lol)
Babolat Syn Gut (got two customers who swear by this stuff...but hey, I stock what people buy, not what "I" like)
Pro Supex Maxim Touch
Weiscannon Silver String
Topspin Cyber Blue
Kirschbaum Pro Line II
Solinco Tour Bite
I also have reels of:
Genesis Spin X
Pro Supex Big Ace,
Poly Star Energy
Gosen Polylon (a mistake, but a few high schoolers like it)
Mantis Comfort Poly
Like Ash Smith, I don't mark-up the string per se; I use the price of a set which serves as my bonus (of sorts) since I only charge $10 for labor regardless of string type.
Need help finding lost dog: walks with a limp, recently castrated, can only see out of one eye - answers to the name, "Lucky".