For a rational investor it would make sense to bid above "market" price. There are many markets, and those markets have a limited volume of coin to sell. Buying 30k coins would have a big effect on the price of any single market.

Bitstamp, which says "world's leading bitcoin exchange" about itself can't sell you 30k coins right now. Oh, and bitcoin exchanges have a history of.. let's call it.. problems.

A rational investor who wants to buy a large volume of coins would certainly bid above "market" price for coins handled by a reputable seller.