Question: If anyone who's been booted talks about Kingsman, they and their family will end up in a body bag. How come Charlie escaped that fate? (00:30:52)
Question: Harry told Dean he had enough information on him to have him locked up for life. What information was this?
Answer: CCTV surveillance and such like. And a possible kingsman informant embedded in the gang leaking incriminating info. Or police informer who reports to kingsman. Or, y'know, he was lying.
Question: What was the point of the "shooting the dog" test?
Answer: It was to test whether the candidates were willing to do whatever it takes to get the job done. If they were willing to shoot the dog they had been caring for, it means they would be willing to make a tough choice in the field to complete a mission.
Answer: To see who is kind hearted or cold blooded, a spy has to make tough choices in the field.
Answer: Details aren't given, but it seems that Dean is involved in local crime along with the gang that hangs around with him. Even if Harry is bluffing, and doesn't have specific proof, it is clear that he is abusive and he has the recording of him threatening Eggsy.