Buehrle does have a reputation as a very honest person, so if he says that someone in the Marlins FO verbally "promised" him he wouldn't be traded, it may very well be true. However ... unless we hear a recorded conversation between them or a stenographer happened to be in the negotiations, we can't confirm this. I wouldn't put it past Samson or Loria to do that, though, in order to get what they wanted in Buehrle signing.
Yea, he doesn't seem like the type to talk crap for the heck of it. I don't blame him for being upset.