When an item has an "InstaBuy" logo or link, it means you can purchase that item before the auction closes at the price indicated. (Note: the price may not include shipping so be sure to check the listing or ask the seller).
The InstaBuy link or logo will only appear if the reserve price has NOT YET been met or if the current bid is less than the InstaBuy price.
By submitting the InstaBuy form, you are making a binding contract with the seller to purchase the item according to the terms listed in the auction listing.