@OP, are you going to sell it for one person (ewxlusive) or to any one who wants to buy it? Also are you going to offer after sale assistance in case a bug is found?
Any one interested in buying this script must think thoroughly because startinh a casino business is not only about having a working script/website. This should be the last thing you think of. The competition in this field is tough and starting with a modified pre-made script isn't a smart move. Just my opinion.
So you have a completely correct opinion.
Who in their right mind, not knowing anything about how the entire online casino market works and generally only familiar with programming, or understanding anything in the development of gambling, will buy such a script??? Moreover, those who could be interested in such a program have long ago had entire libraries, repositories of the corresponding scripts.
So the OP's mistake is that he will never find a buyer.
If only OP is lucky and some crazy eccentric buys his program with a fool, and even then, just throw money away.
Because such a buyer still does not know what to do next with such a purchase.
Yes, and everyone's program will be different, of course, so it will be difficult for those who buy such scripts to be able to move forward, what to do and how to develop it.
So it seems impossible to find a buyer who is really serious about continuing a program he doesn't understand.
Meanwhile, without having to buy scripts that are made and sold by OP, someone can make the same program on their own so that it will be easier to run and develop to continue going forward.