Just to confirm your suspicions, Civil Code Sec. 1748.1 does in fact prohibit the agent's surcharge for the use of your credit card. The law is current, and has not been preempted or modified by any court deision or federal law.
Moreover, 1747.02(e) provides that: "'Retailer' means every person other than a card issuer who furnishes money, goods, services, or anything else of value upon presentation of a credit card by a cardholder." This clearly would include a real estate agent/broker offering vacation rental services.
So, if the agent refuses to withdraw the surcharge, then you would be entitled to demand a refund, which if not received within 30 days, would further entitle you to sue for triple damages (three times the surcharge, plus attorney's fees and costs, if you choose to hire a lawyer to sue on your behalf).
Even at three times the service charge, it may not be worth your while to sue. But, that's the limit of your legal recourse.
Note: this law is more intended to facilitate class action, by a large number of plaintiffs, all of whom were surcharged for their credit cards. For a single cardholder, the value is limited, unless you're using it to purchase a very high priced item and the surcharge is a percentage of the price.
Hope this helps.
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