Once you upload your design to Spoonflower, you can’t just sell them to people — Spoonflower requires you proof them first. Which is totally reasonable, and I’m sure cuts down on complaints from people who get flawed designs, but you have to pay for the proof, which can add up if you’re doing lots of different colorways of a design.
Luckily, they have some options for ‘fill-a-yard’ which let you use and proof as many as 48 designs in a yard, so it’s not so bad. You can even use that proofed fabric for a product — for 48, you’d be making a cheater quilt, for example.
I’m not a quilter, so I usually go for one of the other options, even though it’s not quite as efficient. You can proof up to 12 designs on a set of dinner napkins, or up to 4 designs on a pair of infinity scarves. And then I can sew up and sell those products, so in theory, assuming someone buys them, I won’t actually lose money on the proofing process.