As much as it pains me to say it, I think you're correct. The OP had a choice to buy from TB classifieds or Reverb and chose Reverb. The OP had a choice to do the transaction via mail or in person, he chose in person. Neither of those choices are necessarily wrong but each has a proper method of issue resolution.
Did the OP get shafted with a hidden defect? Sure looks that way.
Did the seller disclose that the truss was maxed out, rusty or broken? I don't know, I haven't seen either the TB or Reverb classified ad. But based on the OPs postings in this thread I'm going to assume it wasn't disclosed.
So from the side of the story we have so far, it looks like the OP was shafted by a schmuck that feels he can get away with it. The recourse for the OP who purchased the bass in person as a response to a Reverb ad would be to personally visit the seller and request a full refund. If the seller refuses, it should be followed up by a written letter or email outlining the issue, the sellers response and one last request for a refund before it goes to court. If the seller still refuses, it's off to small claims court where a judge can determine the merits of the case and if there was any misreprentation of the product.
Had the OP bought on eBay with PayPal via mail or on TB with PayPal via mail the recourse would be very different and probably with a better outcome. As it sits right now, I'd say the OPs chances of success in small claims court are slim unless the truss rod was specifically claimed to be in good working order.
We haven't heard both sides of the story (and there's always two sides) but right now I feel very sorry for the OP and I sincerely hope he is able to resolve the issue to his satisfaction. What a horrible way to start out the new year.