Buy low, sell high. That's what the savvy investors do. They look at trends, at historical data, potential for improvement and the danger signs of overvalued commodities. I'm talking about fantasy baseball owners, of course.

If you have a player off to a torrid start, do you ride it out or cash him in? If you have a player mired in a season-long slump, do you cut your losses and deal him? Or do you hold on for the long haul?

The most favorable trades are done from a position of strength. That means dealing a player with peak market value before his bubble bursts. Conversely, you can shop for bargains, for undervalued players that are off to slow starts.

Streaking April stars are at peak value ("sell high") and are likely to get worse. Players underperforming their historical averages are buy-low opportunities and likely to perform better as the season progresses.

For Worse: Kevin Youkilis, 1B/3B, Red Sox: The junior circuit's leading hitter is once again off to a roaring start. Youkilis is hitting .414 with 5 HR and a Bonds-like 1.252 OPS. Strong starts are his norm with April and May Youklilis' best months. Youkilis had his best season last year because he did not tail off in the second half as he usually does. Don't get me wrong -- Youkilis is very good, especially with the dual 1B/3B eligibility and that high OBP in leagues that use it. However he is at peak market value right now. You might be able to cash that strong start in for an even better first basemen, like ...

For Better: Mark Teixeira, 1B, Yankees: Teixeira is only hitting .220 but his OBP is .373. That tells me he's not getting pitches to hit. Injuries to the middle of New York's batting order have something to do with that. Alex Rodriguez will return soon, which will help. Teixeira, 29, will reap the benefits of hitting in the homer-friendly Yankee Stadium.

For Worse: Carlos Beltran, OF, Mets: Similar to Youkilis, Beltran is a player I like. He goes high in fantasy drafts -- Homers, runs scored RBI and steals to die for. Also, like Youkilis, Beltran leads his league in hitting, with a .397 average. However, Beltran has only 2 HR, both hit on the road, and only one steal. The improbable average inflates Beltran's trade value. Beltran is a lifetime .282 hitter. The disappearance of Beltran's running game is troubling. Without steals, Beltran is very similar to Magglio Ordonez -- same age and similar hitting career hitting statistics.

For Better: Matt Holliday, OF, Athletics: A lot of people were down on Holliday coming into the season. Moving from a great hitter's park to a great pitcher's park was the reason. So far Holliday has done nothing to dissuade the naysayers. He has no homeruns, no steals and is hitting only .222 at home. Holliday's market value has dropped faster than GM stock. If you have him, bench him for now, especially when he is playing at home. Holliday, soon to be a free agent, hit 25 homeruns and stole 28 bases for Colorado last season. 20/20 seems unlikely, but 15/15 in the final five months of the season would be reasonable and productive.

For Worse: Heath Bell, RP, Padres: Bell was nearly unhittable as Trevor Hoffman's setup man in 2007. In 2008 he was good, but not great. This year, as the San Diego closer, Bell is a monster once again. He has yet to surrender a run in eight games and leads the majors in saves with seven. Not bad for a third-tier closer on draft day. I expect Bell's ERA to climb from zero to near his career mark of 3.48 by season's end. Don't expect a 40-save season for a Padres team that will struggle. Cash out Bell's stock if you find a motivated buyer.

For Better: Brad Lidge, RP, Phillies: I'm not crazy. I know Lidge is hurt and his sore knee will keep him out for a few games. Lidge is in my "for better" slot because his market value is in the toilet. If you have him, hold onto him. If you don't have him, make the owner a bargain offer. Compare Lidge and Bell -- Barring a severe worsening of the knee, Lidge will have substantially more saves than Bell from this point forward.

For Worse: Zack Greinke, SP, Royals: Is Greinke this year's Cliff Lee? He has had arguably the greatest start of any pitcher in major league history. In four starts Greinke is 4-0 with a 0.00 ERA and 36 strikeouts in 29 innings. I think Greinke will approach 200 strikeouts this season, but it will be tough winning a lot of games for the Royals. Greinke's value will never be higher than it is now.

For Better: CC Sabathia, SP, Yankees: Last year Sabathia was 1-4 with a 7.76 ERA in April. In a way that makes his 1-2 record and 4.73 ERA this April very encouraging as a buy-low stock. It's like when a company reports a loss but it's not as bad as expected.

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