Technically, you aren't supposed to sell animals on CL, no matter if it's a BP or a dog or a chimp. It's in the rules, so when you're trying to sell, you're in violation of the rules.

That said, half the flaggers just plain don't think anyone should own pets, it's not about the price tag, it's that you are a horrible person for not being a "forever home" for some "furbaby". Some sincerely think no one should own any animal ever, the PETA/HSUS whackos. Some think anyone who breeds any animal is de ebil. Some think that anyone who owns exotic pets is a irresponsible abuser who turns their pets loose in the Everglades to murder helpless tourists by the dozens. Some think anyone who tries to make money off animals is the most evil person ever!

Flaggers on CraigsList are akin to posters on YouTube. They're morons with no life who think their opinions are more important than the facts. They feel their opinions should be law so they can be pleased with themselves. And yes, they sit on CL to flag anything they don't agree with.