Ebay does prohibit it and if you get caught you may be kicked off of Ebay.
But Pitpat is right, they have options to end the auction for several different reasons and....they wont catch you :lol:
Here is a little something from Ebay...
http://pages.ebay.com/help/policies/rfe ... -sale.html
Offers to Buy or Sell Outside of eBay
eBay prohibits email offers to buy or sell listed items outside of the eBay Web site. Offers of this nature circumvent eBay's fee structure and are a potential fraud risk for both buyers and sellers.
Some examples of outside of eBay offers include:
Using information obtained through eBay to offer to buy or sell a listed item outside of eBay.
Canceling a listing to sell to a buyer who became aware of the item through eBay.
Ending a listing early to sell the item at a higher price to the winning bidder.
Offering to sell an item to a bidder in a Reserve Not Met listing.
Offering to sell duplicate or additional merchandise to underbidders.
It is acceptable for sellers to end a listing early in order to sell an item at the current bid price to the high bidder. Bidders are permitted to contact sellers with requests to end a listing early; however, sellers are under no obligation to do so.
Although outside of eBay offers are not permitted, sellers may be able to sell items to underbidders by sending a Second Chance Offer.