I'm noticing orders from the same areas over and over, so I'm assuming that people who have ordered it are showing friends. A few people ordered a copy before and then ordered a second copy as a gift for someone else. That's what grassroots promotion is all about.
To help nudge that along I have a pre-printed letter I include in the snug padded envelope containing their book order:
Everything written there is true and I'm pretty sure it's helped. Remind the reader that they're special and implore them to share the work with others if they like it. Graphic novels aren't mint-condition collectible investments, they're stories to be read and enjoyed.
Mike Kunkel was a genius when he put "Remember your childhood and pass it on" on the back of his first whimsical and wonderful comic. That one sentence helped solidify a good feeling in his readers and spurred them on to show other people the book. Rey struck a similar chord with the faded library stamp he put in the first few pages of Sharknife... a sense of sharing the enjoyment of comics with others.
Anyways, if you find this tiny bit of advice useful - feel free to show others. :)