When someone tells me they need a spot in a few months and I have a spot open now I tell them:

"I will not know until closer to the date you are looking for if I will have a spot open. However I do have a spot open now and if you would like that spot, there is a $100/week non-refundable holding fee."
This way if they don't want to pay the holding fee I don't have to waste my time interviewing them.