You are correct about the sales tax issues being a bigger pain, especially when the laws don't change, but the BOE's view changes, such as when the you have a letter saying that sales tax should not be collected on private sales from out of state, then now gives bogus reasons as to why you have to collect sales tax. So far I have only talk of legal action with regards to this.
As said the BOE holds you responsible, even if you have false documents stating another price that was paid. It is not worth the risk, which is why I have a policy to stop the transfer in such cases, as well as saying that they lose all rights to the firearm (let them argue that in court). Personally, I would give an opportunity to correct the price and if it does not seem reasonable, I would not do the transfer and I would not ship it to another CA FFL since you would still be considered responsible for the sales tax. There is also the issue of shipping it back knowing that they will try this scam on another FFL.
Correct, a barter is still subject to sales tax on the full value of the firearm, which can be difficult, so it is best to have an actual price.
FFL Transfer/Special Order Dealer since 1993.
Net-FFL list maintainer.
Never try to teach a pig to sing. You waste your time and you annoy the pig. - Robert A. Heinlein