As others have stated, the sales tax being imposed should only be the one levied at YOUR location where the work is produced.
Here in California, it is much more complicated than this. If a customer comes in to our location and pays for something and takes it with them, we charge tax as follows : state, our county and our city tax.
However, if a customer in Califormia orders something over the phone and we use an outside shipping company (UPS for example) to ship the item from our location to the customer's location then we charge tax the same as if they picked it up from our location.
If same customer orders over the phone and we use our own vehicle to deliver the item, then we charge tax as follows: state, customer county and customer city tax.
If an out of state customer orders something over the phone and we use outside shipping service to deliver, we do not collect California sales tax or destination jurisdiction tax. However, the new interstate tax law recently passed may require us to collect destination sales tax if we meet the threshold ($100k sales into destination state per year).
If a customer in the next city orders a sign and we build it here but install it at their location, we charge them tax as follows: state, customer county and customer city tax (assuming we bring the sign with us on our vehicle)
Jerry Brown recently instituted through executive order (no vote) a new tax agency here in California that can get around our state constitution and institute / change any tax it so chooses as often as it likes with no vote from the citizenship or legislature and there is no way to contest any such changes / additions to the local tax system (socialist dream = 100% tax rate). This new tax agency has been feverishly adding new sales taxes to all sorts of things that were never taxed before. One example is LABOR. They are adding labor sales taxes like mad to all sorts of industries. Another notable obnoxious new tax this unelected and unregulated tax body implemented is a real beauty. If a person buys a suit for $500 and pays the $50 sales tax to retailer, the customer now gets to pay the $50 sales tax AGAIN when the tailor at the clothing store hems the pant legs AND the customer has to pay tax on the labor of hemming the pants. To illustrate this better, the customer will pay $500 for the suit, $50 to hem the pants, $50 sales tax on the sale of the suit and $55 sales tax on the $50 tailoring job (yes $110 sales tax on labor!!) for a total sales price of $655 for a $500 suit. This was Jerry Brown's going away gift to all Californians. Try to compete with out of state sellers now.
NONE of the above is tax advice, legal advice, life advice, marital advice or any other advice. I am stating what we have done based on pure ignorance of any tax laws, tax codes, case history. Do not do what we do. Assume we are doing it wrong. CPA, tax attorney and all other professionals should be consulted to get accurate information. This was for entertainment purposes only, and I hope you all had a great laugh.