This may provide some semblance of an explanation.
Per California Board of Equalization (California's Sales Tax Regulator):
"Generally, remote sales by out-of-state retailers to California customers, whether made over the Internet, by telephone, or mail order, take place outside of California because the property is delivered to a common carrier outside the state for shipment into California, and are, therefore, not subject to sales tax."
However, a businesses must charge sales tax if they have a "Presence in California."
"Out-of-state retailers are considered to be engaged in business in California if they have a substantial nexus with California. This includes, but is not limited to, an out-of-state retailer which:
- Has an affiliate operating in California that has entered into an agreement to refer potential customers to the retailer, for a consideration based upon completed sales, by an Internet-based link, Internet website, or otherwise, under specified circumstances, or
- Owns or leases real or tangible personal property, including a computer server, in California, or
- Maintains, occupies, or uses a place of business in California"
eBay headquarters are in San Jose, California. Since you are buying thru eBay they charge Sales Tax to California customers.
Here is the link to the B.O.E. publication
"109 Internet Sales"
https://www.google.com/url?sa=t&rct...pubs/pub109/&usg=AOvVaw2vlNQ5wWOZ0n-ufABd-G7Z