It isn't even legal to reveal both Trader and the Bane...
Revealing the Bane would come before gaining the Curse ("Each other player may reveal a Bane card from his hand. If he doesn’t, he gains a Curse.") If you don't reveal the Bane, you gain a Curse, and can then reveal Trader to gain a Silver. If you reveal the Bane, you never gain anything, and cannot reveal Trader.