It depends on the seller. Ask questions. If it's just some random person who really doesn't know anything about the animal, it's genetics, it's history, etc... Then it may not be a good idea to get it. It all depends.
I've only gotten 1 BP off of CL and I quarantined her for many months in a different room.
I only occasionally use CL to rehome normals and the odd morph if I don't want to ship but I am very adamant about giving everyone all the info required to make sure they know they are getting a healthy and clean animal. I also won't let just anyone who isn't prepared to care for one have one.
So when it comes to CL, just really ask a lot of questions and be sure you can look at the snake in person before you decide you definitely want it. Check the mouth, vent, nostrils, and eyes. These are the areas you are most likely to find problems or bugs.