Actually, you do not need permission to sell what you make from a design or pattern. The only thing that is copyrighted is the pattern and/or pictures themselves. An item made from that pattern is yours to do with as you please. A lot of people try to tell you that you can't make something and sell it but you can. Just don't try to sell the actual pattern itself, that you can not do. And NO, you do not have to give the person who posted the tutorial, taught the class etc., credit if you don't want to.
From the U. S. Copyright office:
"How do I protect my idea?
Copyright does not protect ideas, concepts, systems, or methods of doing something. You may express your ideas in writing or drawings and claim copyright in your description, but be aware that copyright will not protect the idea itself as revealed in your written or artistic work".
So you can learn techniques from a book and make and sell them all you want. I have even seen doll patterns that people sell that try to tell you that you can not change the pattern to suit your needs to make an item. But, if you buy a pattern, you can change it any way you like to make your item and yes you can sell your item and without giving credit.
So, those people selling their finished products on Etsy are doing it legally.