Nobody will stop you from buying an account, regardless of the rank you want, but when you are done, you will never use the account again. Because I believe you will only buy an account to apply for a signature campaign, and when you get accepted, you start receiving payment weekly. Although it may be a nice idea to you, other forum members who know the consequences of such an act will not advise you to do so because it’s discouraging, and purchasing a bitcointalk account will not allow you to know the necessary things about the forum and bitcoin and cryptocurrency at large since you got your account with a high rank. You are only after money anytime you come online, which is not the main reason for the forum.
If you want to buy an account, just say directly that you are looking for someone who will sell an account, but don’t come out and say anything that happens between both of you in the process of doing such shit. However, nobody will tell you the amount of any rank you want; as you can see, this is not a market where you will see every single good with a price attached to it. If you buy an account once you are caught or when they see any changing of hands, the account will be tagged, and you will not get use of it again or participate in signature campaigns.