Zack Greinke would fetch the best return, but Shaun Marcum might be starter Milwaukee looks to deal. (Getty)

The problem with this year's midseason trade market, as anyone in baseball will tell you, is that there just aren't that many obvious sellers. As of Friday morning, 21 of the 30 teams were within five games of a playoff spot, and most of the other nine either don't have much to trade or aren't inclined to sell.

As Pirates general manager Neal Huntington said earlier this week, "You can't buy when people aren't selling."

So you can understand why plenty of teams have their eyes on the Brewers, who are now 7 1/2 games out in the National League Central, after three gut-wrenching losses in Kansas City.

The Brewers have big, potentially-tradable assets in starting pitchers Zack Greinke and Shaun Marcum and reliever Francisco Rodriguez. But they also have strong attendance and a highly competitive owner who said a couple of weeks back, "We always have a buyer's mindset."

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Is this the year the Brewers actually sell?

Teams that have spoken to them say no decision has been made yet, but that the Brewers are at the very least preparing to sell. In other words, they've told their scouts to identify prospects that they would target from teams that could be interested in buying.

At the same time, though, the Brewers are suggesting that they still could become buyers. It's too easy for them to remember what happened in the NL Central last year, when the Cardinals seemed totally out of contention and went on to win the World Series.

Besides, owner Mark Attanasio really doesn't like the idea of conceding.

"The owner likes drawing 3 million," said one baseball man who knows the Brewers well. "The owner is not a give-up kind of guy. He liked last year [when the Brewers won 96 games and went to the NLCS] as much as anyone in the organization."

Still, the Brewers are seven games under .500, and have so many injured players that a comeback this year seems unlikely.

Should they sell, the Brewers appear more willing to part with Marcum and Rodriguez than with Greinke, even though Greinke would obviously bring the biggest return. The Brewers remain very interested in trying to keep Greinke beyond this year, even though negotiations on a new deal are thought to have been difficult so far.

The Brewers will spend this weekend in Minnesota, playing another team that has people in baseball wondering. Rival teams have speculated on whether the Twins would deal Josh Willingham and/or Justin Morneau, with the Blue Jays said to be particularly interested in the Canadian-born Morneau.

So far, the Twins don't seem particularly interested in trading either one, since both are under contract for next year.

And while a source said that Blue Jays general manager Alex Anthopoulos called to ask about Morneau, one rival executive said that means little.

"I like Alex, but Alex calls about everyone," the executive said.