When it comes to evaluating trades there are many factors, and those factors can be multiplied depending on how many players are involved in a trade.
Easier trades to evaluate are 1 player for 1 player and typically different positions or stat strengths. If you had a pitcher that hit the DL recently and someone offers you a quality starter for an outfielder (assuming you have plenty to spare), that is not all that hard to accept. Or say you are falling behind in steals and you have a clear cut lead on homeruns and the offer is Michael Bourn for Mike Stanton. Pretty easy to see the immediate value for you there, eh?
But what if you get a multiplayer offer, say a 2 for 1— how can you determine if this deal will make your fantasy baseball team better or weaker?
Simple, I like to do a little thing called coupling. No, not that definition of coupling but this one: the act of packaging players together in a deal.
If someone is offering you 2 hitters, a good but lesser second baseman, and a solid third baseman for your stud second baseman, you’ll have to drop someone, and furthermore, you’ll have to get both of those guys in your lineup for it to be worth it. In other words, unless it is really worth it, you should not bother.
Now let’s say, for instance, you are offered Chase Utley and Michael Young for Dustin Pedroia. Can this trade work for you? Well, for starters, you’ll need to consider who your third base option is right now. For these purposes, we’ll assume it’s the rapidly aging Chipper Jones. What I like to do is compare the projected stats of the players I have to the players I will be receiving (there are tons of free websites out there if you don’t have your own spreadsheet). If from this point of your season the combined projected line from Pedroia and Jones is 120-28-100-15-.290 and the combined projected line from Utley and Young is 123-29-111-168-.285, then you seem to be better off accepting the trade and dropping Chipper.
Of course projections are not 100% accurate, and these kinds of trades are always subject to the possibility of an injury that makes you regret the trade, but this is what you have to work with. Educated guesses are all any of us have to work with. Just hope your educated guess is more well thought out than your league mates.