You may have seen this viral story about an employee from Urban Outfitters who denied a trans guest the preferred changing room. In this case, the customer who identifies as gender fluid and uses the pronouns they and she was initially taken to the wrong dressing room, away from their friend who is female-identified. The customer eventually was given a dressing room in the women's area, but far away from their friend.
Urban Outfitters' response wasn't very satisfactory and deferred to the laws. In California (unlike other places like New York City), there is no law requiring stores and restaurants to let guests use the bathroom and changing room that reflects their gender identity.
In this case, the employee's best response would have been to ask the guest which changing room they prefer. Asking may seem awkward, but it's actually far less awkward than the ensuing response when a mistake is made. The worker could have simply said, "which changing room do you prefer?" and let the guest decide which is more accurate given their gender identity.
photo by Walt Cessna