The problem, is that bustabit never actually provided a license. "Umm... Text file" doesn't cut it for real world situations like a serious buyer wanting to check in to things before making a purchase (Looking at the business revenue, number of users, gambling license, SOFTWARE LICENSE).
It is my understanding that AGPLv3 itself is the license, and a written acknowledgment of sites that have purchased a copy of the software (e.g. https://bustabit.com/license.txt) is enough to show who is exempt from the requirements of the license. If what you wanted was a license certificate or document, I'm afraid that's something you should have asked at the time of purchase. But anyway, as long as you comply with the terms of the license, like making your code open source, you are free to do all the things you mentioned. You only need to purchase a commercial license if you don't want to share your code.
I hereby call out Bustabit with this question publicly - For the integrity of Bustabit's name, and quite frankly, so people don't get scammed (Because the only buyers that readily accept "Umm... Text File" for a license seem to be ones that would use the purchase to scam others...) can a bustabit licensed website be surrendered (Domain control given to Bustabit & Domain delisted from the "license text file) to Bustabit for a refund of the original license cost (2 BTC) ? And if Bustabit isn't willing to provide a full refund for a product that was sold and never provided - is Bustabit willing to provide a partial refund and finally if so, what would the amount be that they would in fact provide for this situation ?
I would argue that it's quite the opposite, and sites serious enough to invest in a license are less likely to scam their players. But no, I won't be issuing refunds for the same reasons I mentioned above.