I'm just getting in to the pipes myself, mainly because I didn't even see any listed when I first started buying mods and didn't realize they existed, because they just weren't being carried by many. Even my local B&M's with a large enough mark-up to let things sit a while, only carry a few and they are in the back of the cases where you can hardly see them.
Anyway,... my suggestion is to carry the ones that actually look like pipes... wooden body, 510 at an upward angle, etc.
I'm not buying any hardware until after vapeXpo, but I'm sure I'll be posting picks when I finally make a decision on my first pipe.
Here are some names of ones on my list...
Kamry K1000 Kit
Smok Chaser
Sherlock Wooden e-pipe
There are actually quite a variety out there once you look. Obviously, what to carry is a question only you can answer, but I hope you see increased sales from any that you do carry...