Identifying the voice as fake is not the main defense against these scams, though. The main defence is recognising the situation and taking a step back to double-check. Primarily the scammers are trying to stop you from engaging your critical thinking by putting you under pressure and a very useful skill in life is recognising those situations and pushing back on them.
If an expert can't distinguish, it has absolutely nothing to do with being "stupid" or not. So send them that, maybe.
If they are still stubborn about it, then thank them for contributing to the future funding of Scam the World With AI.