Bargain buyers were out in force in the Hamptons over the summer, turning the period into the strongest summer season for sales since 2006.

But median prices fell by 10% during the third quarter compared with the year-earlier quarter, as sales of the most-expensive homes—mansions that often come with ocean-front bragging rights—lagged behind, according to new market reports.

The highest price sale during the quarter was an $18.6 million sale of a house in Wainscott near the ocean. That was far below the peak price for the year—a $28.5 million ocean front house in Southampton Village sold by Marc Rowan, a co-founder of private-equity firm Apollo Global Management. That sale closed in January.

Susan Breitenbach, a top-selling East End broker, said that since the third quarter ended Sept. 30, there have been “a lot of high-end people” looking at houses. She said that a spate of big deals, including some topping $20 million, would close before the end of the year.

“You are going to see a lot of properties trading during the last quarter,” she said.

The market reports show that a sales rebound in the Hamptons that began earlier this year, especially among properties priced below $1 million on the South Fork, is still going strong. Those properties are often a cottage or small home, far from the beach.

Analysts said the rebound in deals sub-$1 million deals was driven by falling interest rates and declining prices as enticing properties pushed more below the $1 million level.

In the peak spring season, total sales of 539 were the highest for any quarter since 2007. In the latest quarter there were 405 sales recorded, the highest for the third quarter since 2006, according a market report prepared by Jonathan Miller, an appraiser and president of Miller Samuel Inc., for Prudential Douglas Elliman.

The median price of a Hampton’s home was $765,000 In the third quarter, down 10% from both the second quarter and the third quarter of 2011, Mr. Miller’s report said. That was still 30% below the peak prices during the boom years.

The average price was $1.43 million, down 18% from the year-earlier third quarter.

Gregory J. Heym, an economist who prepared Hamptons market reports for Brown Harris Stevens and Halstead Property, said that closings were likely to pick up toward the end of the year, as sellers rushed to complete deals before increased capital-gains tax rates scheduled to go into effect next year.

He said that 60% of sales were below $1 million in the latest quarter compared with 57% during the same quarter last year. At the same time, there were 19 sales of $4 million or more compared with 23 in the year-earlier period.

Mr. Miller said that as elsewhere inventory in the Hamptons has been falling, leading to the possibility that prices may rise in the months ahead, even without an improvement in the outlook for the economy.