...as no Beta software should be sold, as that’s entering into a (grey) legal area between the retailer, and the rights and expectations of the paying customer.
I think you are a bit mistaken about this. Many companies have a practice of releasing “paid betas”, for various reasons. Whether you agree with the reasons or not doesn’t really matter. The customer actually agrees to pay for the right to use the software when it’s in beta version.
And there is no “(grey) legal area” whatsoever. There is no law against charging for betas. Nor is there a law that defines what you must describe as a beta. And just because some customers might not think it’s “right” to charge for a beta version doesn’t make it a “grey legal area”. Companies can charge whatever and whenever they want, and the customer has no rights in the matter.
If you owned a software company, and had customers who went nuts over your product, and would gladly pay for what they considered the privilege of using your software, even if it was in “beta”, it might make a lot of sense for you to charge for your beta release. And there’s nothing that says you can’t.
BTW, for those of us who are familiar with Lightwave, we’re very much aware of how Newtek charged a ton of money (over $300 I recall) for people to participate in the LW 10/Core paid beta. Well, except for people like me who told them to go jump. Of course there were a lot of guys who fell for it and considered themselves lucky. Go figure.