Why would you go to all that effort if they don't want to play with you in the first place? If they really wanted to block you, they'll do it through their lawyers.
It's also very easy to differentiate between a crawler and a user. But they don't even have to do that. Blocking the entire AWS ip range isn't hard either. I doubt any craigslist users browse the site through AWS :)
And you may convince them to join you after all, like YouTube and the media companies they parasite off of.