Thirty for a bumblebee hatchling seems like a screaming deal but nothing I'd just walk away from. Especially if it's by the exit on the last day of an expo. Last Repticon I went to I got a het pied hatchling from a guy that was telling us a story about how he had a 1500ish gram female pastel, never locked or paired, about 2 years old. At one weekend show he had her in a glass case and wrote (free, see xxxx). He said NO ONE even asked him about it, they all just pointed it out and laughed. He ended the weekend with taking the snake home...
I could totally see someone having a lot of bumblebees or not needing a male bumblebee at all, so instead of them saying that they'll hold on to it and wait to get the 100-200 they'd hope for it, if someone will pay the 30 at the exit then it's one less snake they have to bring home, take care of, and feed.