This is very subjective, and really depends on your market, and demographic.
To start out with/a basic "safe" stock would consist of:
Basic/standard synthetic gut: Prince SGw/DF, Wilson Stamina, Gosen OG Sheep Micro, Wilson Extreme, Babolat Syn gut, etc
Standard/basic Multifilament: Wilson Sensation et. al
Higher end Multifilament: Gamma Pro, NXT, X-cel, Biphase, NRG2, etc
A set or two of gut (rarely requested)
Polys: (This is probably the category where you need to research.
Sub categories of polys would be:
-Soft/more comfortable Poly: Cyberflash, TCS, Signum PPP(P)
-Cheap/Durable poly: Gosen Polylon, etc
-"performance" and/or textured poly
I'd also throw in a set or two of Kevlar for those SERIOUS string breakers, and I'd suggest stocking something like an Isospeed or a Head Rip Control style polyolefine string for players who need something more durable but aren't willing to sacrifice comfort (read as: a stop gap between a syn gut and a poly string). Most people love/hate these types of strings.
Edit: Also I'm not sure of your 30... is that $30, or 30 different types...?
4x Dunlop Bio 200 L // Babolat Sensor
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