The previous tennants are obvious smokers and the house had that stale aroma (is that the right word? :/) to it. To the houses' defense, it was more than probably the furniture owned by the tennants that brought the smell, as smokers clothing and personal affects often do, but changing the carpet might go a long way to remove it from the house.
I'm not sure when we'd be moving in if they do decide to go ahead with the carpet, hopefully not too much later than 28 April.