So basically:
- if the price is 5$ at launch or more you will obviously keep your tezzies and payment will be refunded to the buyer without any penalty on the seller.
- if the price at launch is below the deal that you make now, then you will sell your tezzies to the buyer at much higher price.

So you will guarantee that you will be the winner in all cases. That's unfair.

In all fairness, you should also put a money in escrow to compensate the buyer in case the deal is withdrawn by you.