Check out this guide for out of state retailers...”What you gonna do when they come for you!”
Sales tax applies to sales of tangible personal property made within California. The use tax applies to the use, storage, or other consumption of tangible personal property purchased from a business located outside the state for use in California. As a registered out-of-state retailer, the tax you collect will generally be the use tax.
If you sell property to a California customer who plans to resell the item(s) in the normal course of business, you are not required to collect any sales or use tax provided the sale is properly documented. However, you may be required to register and file returns if you have nontaxable sales.
In California, all sales are taxable unless the law provides a specific exemption. Similarly, use tax applies to the purchase of tangible personal property purchased outside of California that will be used, consumed, stored, or given away in this state, provided no tax was paid at the time of purchase.
If you drop ship items into California, you may be responsible to collect and report the tax.
A drop shipment generally involves two separate sales. First, a retailer not engaged in business in California, makes a sale to a California customer. They are the "true retailer". The true retailer then purchases the property from a supplier and requests that supplier (the drop shipper) to directly ship the item to the customer on their behalf. The true retailer never physically possesses the property.
When a true retailer uses a drop shipper that has nexus in California, the drop shipper becomes the retailer and they are responsible for collecting and reporting the tax. Tax is based on the amount the retailer invoices the California customer.
The retailer may accept a valid resale certificate from the California customer if the property is being purchased for resale. For more information, see regulation 1706, Drop Shipments.
For more information click here: https://www.cdtfa.ca.gov/industry/out-of-state-retailers.htm#DoingDailyBusiness