I must say that while I agree, I think that in this situation you (or your company) greatly profited from the bad planning of your client.
Put another way: your client also paid a lot of money for their jumping-the-gun, but I'm sure this was calculated into their sale price, and was probably not bad planning at all, from their perspective.
I don't mind faking screenshots to drum up business and test how viable an idea is, but if you accept money for software that doesn't exist, and then demand a ridiculous turn over time from your development team (whether in-house or outsourced), then you're scum.