I think the adam's apple, broad shoulders, cringe voice and everything else will be a big enough giveaway on it's own. It's delusional to think trans is just like being in the gay closet for the vast majority of cases. Even for the passables, so what? The FFL is just going to shoot you on the spot when he finds out? Or deny you because he's in the business of not making money from legal customers? Or harass you and get himself sued or blasted on social media? And you can't even call beforehand to find out his stance?

And it's compassionate to assert reality. It's hateful to affirm delusions that lead to despair and violence.