Please help, I have a huge dilemna on my hands.

[Evenstar]

While I agree that that's poor substrate choice, the uth and heating are laughable and potentionally dangerous for the health of the snake, and me personally not being partial to fish tanks for larger boids I disagree about the animal appearing stunted/starved. That's not a true red tailed boa: its a common Colombian BCI which averages 5-7' and based on the body shape and tone of the animal it actually looks well fed to me. I would suggest it to have two hides and a better bowl but even bowl wise I don't give my boas large enough bowls to soak in and they're fine. This guy needs some basic husbandry changes but I wouldn't call it horrific, I've seen much worse.
I can't speak for Florida laws but I would see if a rescue would be interested in taking in the animal: for selling the current owner could always argue "I'm rehoming it, not selling" too unfortunately.

I agree completely. The snake looks more or less fine to me. I am a bit appalled at the dangling heating pad, but I too have seen much worse.

To be brutally honest, my suggestion to you, is to quit looking at Craigslist.

This. If you're going to browse craigslist, you need to be prepared to see this kind of thing. It does suck, but we can't save them all.