I didn't know people got so little feedback. I've only had one person not give me feedback, and maybe she's unsure how. Actually, when I first put things up my dad bought something (hee, hee), but he had no idea you left feedback on here, and I ended up asking if he would.
I like Justweddingbouquets's idea to ask them to leave feedback through Etsy. If they say no or they don't want to, just drop it, though. Even if half of your buyers leave you good feedback, it's still good feedback, you know?
Also, I sometimes don't leave feedback right away, if it's jewellery or something else I wear, I want to make sure it doesn't break or anything.
And, as a buyer, you leave feedback first. But, as far as I know, there is no way to know if you've gotten feedback, except to check. Maybe if you send a message saying you got your item, they will check to see if they have feedback, and then leave you some in return.