Below is the list of precautions that you should take when you buy an account:
• Do not contact support
By contacting support on a purchased account will be risking account getting locked/banned, it's recommend it not to contact support unless it's absolutely necessary.
• Location cooldown
Recommended to wait around 24-hours before you login to the account after purchasing it and do not share your account with others.
• Name change & in-game purchases After buying an account It's recommended to wait 10-days before changing it's name and before making in-game purchases (gems, goldpass or skins).
• Avoid getting scanned
Pushing to top players, playing CWL in High ranked clans (Champ 1), getting reported a lot by other players and mentioning buying/selling in clan chat are all things you should not do to stay low and avoid support checking/scanning your account and possibly lock/ban it.