I honestly don't see how that's a problem. If the design are by you yourself, you still have rights over the design. Even if someone bought it.
But I've come across this problem before as it tends to be a heated black and white debate. As some people believe that once you buy a design that all owner rights now belong to said person. While others believe that because they made it, they still have say over what their design can be used for.

I think maybe it's a matter of preference and what you think is best for yourself.