sales tax only paid once

When a customer order a piano from a piano manufacture by mail order directly, the customer will have to pay CA sales tax to the piano manufacture, who will send the sales tax receipt to the state of CA. 

However, when a piano store buys a piano from the same piano manufacturer, the piano store as a "reseller" does not pay California sales tax.  The Califronia sales tax is only paid when the piano store sold the piano to a customer.  That customer, since he already paid sales tax once on this product, is free to sell the piano without collecting sales tax from the next buyer. 

Hope this helps.