My understanding of the GPL is a bit murky, but I think that as long as the cost is reasonable, and the source code is included or made easily available, it's legal do distribute works for a fee. That said, I don't know about auctioning. And it seems that the source code is not included...
I take issue with the renaming of the program, which is certainly questionable in my book. It's probably the only modification made, but certainly is a modification, and makes it subject to Copyleft. All of the screen shots show 'Game Creator' in the titlebar instead of 'Construct'.
It's certainly shitty in my book as well.