How can amazon not charge tax and shipping on most of the products. Whats the business model?

Answer 1

They don't charge sales tax in most places because in most states, they don't have a physical facility.

They make their money from markup on the items they sell. They usually don't charge shipping on orders over a certain amount - they're already making their money on the markup, and apparently have decided they'll get enough extra business by not charging shipping, or will get people to order an additional item to make the $25 limit, to make it up for not charging shipping.