According to the interview this morning, the car was not modified when it was sold. Also Malvo was not with Mohammad at the time he looked for the car, just the co-owner. Mohammed was not very talkative, spun a line about being from Jamaica, then started to talk with an accent. Salesman said he remembered him because after saying he was from Jamaica, and then saying he was from Canada but of Jamaican ancestry, he then pulled out a DC driver's license. Salesman said he could not engage the guy in conversation.
FBI merely asked him if he had sold the car, and asked him who bought it. Apparently Fox asked more detailed questions than the FBI.
*sigh*