BHW, I am disappoint.
Okay okay, lets pimp your supposedly cute GF's stuff.
Forget the panties. $10 - or even $20 a pair won't really cover her costs. Cute panties (the stuff that sells) is hard to find for less than $10 a pair. Then you've got to wear them (time consuming), package them (more costs - snap lock bags essential) and then ship them. You need a higher profit margin to make this one worth your time. OH YEAH, then there's the issue of every man and his dog selling used panties online. The supply is MUCH larger than the demand. Its a wash-out. Time to change tactics.
So instead of selling panties, lets look at selling used clothing. Large, disjointed communities. Too hard. Focus in on one particular niche.
Heads up: you want socks. You want all the socks. You want to go to all your friends and family, tell them you're doing some stupid art project and you need all their old socks THAT HAVE HOLES IN THEM. Go and gather up all the nasty, worn out socks you can find. WASH THOSE NASTY SOCKS FIRST. Let them dry. Throw pair after pair of socks at your girl, make her wear them and photograph them all. Offer all those socks for sale with various prices - the longer she wears them before shipping, the more they pay. You can get at least $20 for a pair of those socks (which you got for free), and ship them flat in an envelope in standard mail. MINIMUM $20.
Yes, I hear you bitching about where you find a market for this stuff. The foot fetish community is enormous. The foot sniffing community likes the scent of feet. Ladies feet. Sweaty ladies feet. They are polite and they pay - no creepy nudity, no stalkers, just a bunch of old socks. I've done this for quite some time and never had a bad deal from it.
Go start at footsniffing dot com. They've got a sales section. Use it.
Last point: you'll end up selling more socks than you can handle. Don't make it look like a factory. Wear those girly socks underneath YOUR socks when you're out doing stuff. You'll get twice as many stinky socks in half the time. Put one super-awful smelling pair of socks in a snap lock bag with two clean pairs, put a bit of water in, microwave that bag for a few seconds and let it settle overnight. Instant stink-socks.
You'll be doing just as much work as your girl here, so it doesn't really qualify as pimping. BUT sock-pimps are still pimps. Get your pimp on, son.