There have been a few times over the years where someone has posted something on one of my communities that was inappropriate and then they will say that someone else posted those comments under their account.
This is a tricky thing because it’s easy to blame your teddy bear for that glass of spilled milk. At the same, I do try to take it as an honest admission if it sounds like one. It all depends on what they did, what they say and how much of a history they have on the community. If it sounds feasible, I am usually inclined to at least give them one chance on it.
Meaning that I’ll accept that explanation this time. But, I will still make a note of it in their documentation and make sure they know that their account is only supposed to be accessed by them. No matter what, the account holder still has responsibility for what is posted under the account.