First of all, it is a rule that to buy or sell on the EE you must have valid contact info. This goes for having email and IM functions turned on as well so the other party can contact the buyer / seller.
Go ahead and respond to your ad even though it will be an early BTT. In the reply post that the buyer must turn email and IM functions on and that you have cleared this post with a MOD before posting so your ad does not get locked up.
Personally, I don't know if I would do business with someone that I could not contact through the board. Then again, maybe it is a newbie that just hasn't figured it out yet.