I've been filmed a few times. I always smile, ask them to make sure they have a clear view and a good picture, introduce myself, and then describe the situation and the decision I've made calmly and in a friendly manner, together with my reasoning. So far, it has always produced positive results.
I will say, however, that if I'm dealing with, say, an invalid Railcard discount, when I explain that an excess is payable, if the customer just pays the excess and we can both get on with our day, then all is well. However, if the conversation becomes challenging, that excess- which is, after all, discretionary, and the discretion is mine and mine alone - quickly turns into a travel incident report, for someone else to deal with and decide upon.
The same goes for filming me : if it's a happy exchange, I will play along. If it's not a "happy" exchange, then I will remain friendly and professional, however everything will be by the book, up to and including police involvement.
Unhappy exchanges are almost non existent for me: I try to listen, to understand, to empathize, to carefully check facts. The only bad one I ever had resulted in police meeting the train, and the officers who attended offering the passenger a choice between arrest on the platform, or providing verifiable ID to myself together with deleting their phone footage. All over a grown man on a child ticket.
A point to note is that on a train fitted with CCTV, the existence of the CCTV warning stickers within the train is considered sufficient, and therefore it is not necessary to inform the passenger you are filming them on a body cam, as it is an extension, if you like, of the on train CCTV. On the rare occasions I use my bodycam, however, I always inform the subject that it is activated.
In this life, you reap what you sow. This applies to both Crew, and Passenger. Worth bearing in mind.