Timed ending or bidding extended after somone bids?

Do you prefer auctions which end at a certain time like on eBay or would you prefer the time limit to be extended by a minute or two after someone places a bid?

Personally, I like to snipe things.

Do you think that auctions where the time limit is extended after someone places a bid helps the seller earn more?

Timed like on eBay.
Yes, extensions jack the price up, just like with penny auction sites. But to me this leaves a lot of room for dishonest shill bidding.