You're right, you can't "sell" GPL software. What you mean by "sell" is "grant a license for usage" and that's exactly what the GPL or a similar FOSS license does. So the two things conflict. Really you're describing a situation that the GPL is not designed for.
Your desires are more inline with Microsoft 'shared source' type of situations.
The GPL and the FSF's world-view isn't particularly aligned with what you want (I believe). Either use the GPL and live with the constraints, or use something else. Something else's that come-up in a GPL but commercial context are:
a. Service or Support. You've said you want to be paid for creating the software and not for providing services, so this one is out. Note that SaaS is now the easiest way to achieve what you want.
b. Dual licensing. You said "you can't depend on GPL software then". Well yeah, because GPL is about a commons of equals 'sharing' and you want to charge for sharing - so you don't get to use other people's stuff for free. Seems fair to me.
But, your actual concern isn't really valid - there are lots of things you can write without depending on GPL software. This is probably more realistic than you think.
c. Open core. Someone described this to you earlier, I think.
d. Validation and/or IPR. Probably outside the boundaries of most individual developers. But think of the way that Java is licensed on the basis of it being a 'valid' implementation and then IPR and trademarks.
Your desires are more inline with Microsoft 'shared source' type of situations.
The GPL and the FSF's world-view isn't particularly aligned with what you want (I believe). Either use the GPL and live with the constraints, or use something else. Something else's that come-up in a GPL but commercial context are:
a. Service or Support. You've said you want to be paid for creating the software and not for providing services, so this one is out. Note that SaaS is now the easiest way to achieve what you want.
b. Dual licensing. You said "you can't depend on GPL software then". Well yeah, because GPL is about a commons of equals 'sharing' and you want to charge for sharing - so you don't get to use other people's stuff for free. Seems fair to me.
But, your actual concern isn't really valid - there are lots of things you can write without depending on GPL software. This is probably more realistic than you think.
c. Open core. Someone described this to you earlier, I think.
d. Validation and/or IPR. Probably outside the boundaries of most individual developers. But think of the way that Java is licensed on the basis of it being a 'valid' implementation and then IPR and trademarks.