Theoretically, if you buy inv key from someone and staff will find out about it, you will get ban, along with person who sold it to you.
Most cheats providers (where inv key is required) ban something like this, you should get this key for free, but people consider it as good business...
I suggest not going into buying accounts or invites. You could either get scammed, get banned from the cheat or have a bad reputation for buying invites or accounts.
Even if you don't get banned from let's just say skeet.cc/gamesense.pub then you just wasted 400$ on a cheat for a game from 2012.
Theoretically, if you buy inv key from someone and staff will find out about it, you will get ban, along with person who sold it to you.
Most cheats providers (where inv key is required) ban something like this, you should get this key for free, but people consider it as good business...