@Carmie0, go with your gut. If he hasn't bothered to give more info, and discuss why he is visiting etc., you can just decline. Air will ask you why - you can just say you were not comfortable with the guest and initial communications were poor.
@Carmie0, one more thought.... you have a very pretty profile picture on your site, and I would be wary of single men potentially wanting to stay in your place for nefarious reasons without wanting to bother taking them time to engage first in some discussion about their trip etc.