It seems counter-intuitive, but limiting who you sell to is actually a great way to amplify word-of-mouth for the item. But it all starts with having a product worth talking about.
A company that's figured this out is OnePlus.net. They let their fans do the marketing for them. Anyone that purchases a One Plus phone is given invitations to give to their friends and family to buy.
As always, I'd love to hear your thoughts on this topic and any other interesting marketing-related musings.