Parity killing off the seller's market

Jeff Samardzija is one of few "commodities" on a clear seller. But even the Cubs haven't budged yet. Brian Kersey/Getty Images

The volume of calls and text messages between general managers is growing as teams look to improve through trades, through adding help from outside of the organization.

But as has been noted many times since Major League Baseball expanded its playoff field from eight to 10, the extra wild-card team reduces the field of potential sellers, because more teams have hope and reason to wait to break up their teams.

There is another factor depressing the trade market as well, according to some executives who have taken the pulse of rival evaluators: parity.

The Oakland Athletics have been a great team this season, with the best record in the majors at 44-28 and a run differential of plus-132. The Giants own the second-best run differential -- 85 runs less, at plus-47. Twenty-six of the 30 teams have run differentials ranging between the Giants' plus-47 and the minus-40 of the Texas Rangers and the Houston Astros