If you put your design on one shirt you have to deal with these issues:
1. You will either lose money on the cheaper shirts or overprice the shirts that have a high base price. Because Zazzle uses a percentage based royalty, you can't easily correct this situation. Lets say for instance you want to make $5 on every shirt you sell. Okay, to make $5 on a value shirt you have to give it a commission of 28.1% now if all your shirts are set at 28.1% then your black hoodie will sell for almost $54. That's about $15-$20 more than what folks expect to see on the sticker price. That and they're expected to pay shipping too.
2. You have to assume that every customers knows to use the Zazzle browsing feature to find a shirt they like. In my 2 years of experience, I didn't start selling shirts at Zazzle until I listed a lot of shirts folks normally buy.
In my opinion, web shoppers aren't used to the idea of there being a design and they can put it on whatever product they like. So when they see that one shirt, or even four shirts, they figure that's all that's available. Zazzle hasn't found a way in the interface to make this more clear and even if they did, I don't think it would make the shopper more comfortable with what they are buying. They don't like buying something that's made up on the fly, they want something they believe already exists and is just waiting for their order to get shipped to them.
Funny Graphic Shirts