There is still plenty of demand for housing. Potential buyers, both young and old are trolling listings online and packing in to crowded open houses. But they are not rushing to write offers. The culprit may be sticker shock. While buyers in June were still requesting tours at the same rate as May, 11 percent fewer were putting pen to paper on an offer, according to Redfin, a real estate brokerage which surveyed 15 major metropolitan housing markets. The same is true, however, throughout much of the nation.