yeah thats sad but true, because it somehow limits you in terms of selling your product. you must also let them see your sales figures, if you agreed to such a contract! e.g. make no more than 5000$ type of things...

i'm shure dexsoft will not do this, but believe me others are making use of such stuff in other ways and try to squeeze the last inch out of you for minimum work they did.
so if you used many outsourced art assets, you may end up making no money at all, because at the point you break even and actually make some money, they do want to see much more. thats why i would always only buy if i can calculate with fixed numbers like 1000$ for commercial license, 100$ for indie.
the thing is once you sell your indie game to a publisher it ends for you beeing indie.

however again, i doubt dexsoft will do this, its just a general word of advise based on real experience i would wish no one else.