If you’ve done your research, you won’t be ripped off. Alternative a pproaches are famous for giving more than necessary to help people. On the other hand there are always a few unscrupulous people out there, both buyers and sellers.
If the worst comes to the worst, return the product and ask for your money back. Most teachers will be happy to return what you’ve paid (less postage) if only because, although you might not have liked what you bought this time, you may like something else they have to offer– if you get good customer service, you may come back later. It’s in our interests to treat you well– and most of us are good people, too, so want you to be happy.