It's called 'bidding frenzy' and we all love to have it.
Your bidders are grownups and while you may think they are bidding above the norm, your item may be harder to find than you think.
Possible outcomes include:
The buyer pays, you ship, he is happy.
The buyer does not pay, you open an Unpaid Item Dispute. You get your selling fees back and he gets a Strike, Neither leaves feedback.
You offer the underbidder the item as a Second Chance Offer. He pays, you ship, he is happy.