I have a couple of Zazzle stores (heArt-a-Day, Vintage Collage) and I used to have a Cafepress store. I have maybe made $20 in the three years that I've been trying this. I thought that perhaps I had the wrong subject matter. Meanwhile, I have a stash of decent photos of some everyday things which are - to my surprise - viable keywords, so I thought I'd make a new shop using them. Most of the good keywords are already used for shop names, so clearly there are other people doing their keyword homework and hoping to make a buck. But are they really getting any sales?
Because while doing my keyword research, I found something that astounded me. According to my keyword analysis tools the numbers for keywords t-shirt, sweatshirt, greeting card, card, mug, poster and print don't add up. Supply far outweighs demand (what minimal demand there is). So there may be lots of people looking for a picture of a cow jumping over the moon, but they aren't looking for any of those things to put it on. So why would they buy them?
The only way I can see that this would really work is if you already have a fan base for your images and they're looking for something else to put them on.
If you are somebody who is making a nice little income from your Zazzle or Cafepress stores, please let me know. Otherwise I am taking the stance that it's your basic carrot-in-front-of-the-horse marketing scheme that most of us are falling for resulting in no real sales or even traffic.
I really want to believe it will work, though. After all, it is no inventory! print on demand! we'll just send you the profit money! And at least on Zazzle it's completely free.