In Philadelphia, with a four and a half month median time on market from listing to contract, prices are down by 5.3 percent.

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To hold onto the contract overnight, it's necessary to post a margin that depends on the contract's volatility and is set by the listing exchange.

FORBES: Money & Investing

Merely five days after a listing flyer hit my mail box, the unit was already in contract for the full asking price.

FORBES: Surprise! Some Cities Are Actually Experiencing Housing Shortages