Even before Marshall's injury, Maclin was getting better #'s than Marshall. Without knowing what kind of league this is, can't say in the long run if this a good/bad trade, but in the short term, it's bad on Team A. That said, shame on Team A owner for letting a deal sit there for three/four days and cudos to Team B for accepting it. This one, I'd just let go to bad trading on Team A's part.
Every owner has a different value system, so can't be 100% sure, so in a dynasty/keeper league, would have to wait & see; BUT, in a redraft league, OH YEA, I'd be questioning it as it definitely rrreeeaaakkksss!!!
That all said, like most experienced FFers, we all have made both good & bad trades, but in most cases, we think they're good/great at that time and there are those in the league that may not agree. Case in point, I took over a team in a brand new dynasty league that the original owner resigned. Did a trade for J.Charles and gave up Steven Jackson & Matte Forte (now there were other players & draft picks involved, but these were the main ones). Now, in my value system, I'm not a S.Jackson fan because of his injury history & age (plus he cost me a championship by being unavailable) and under no circumstance will I have a Bear, Viking, nor Lion on my team (can you guess who I like) and most importantly I think J.Charles will be the next Priest Holmes, so I have Charles valued extremely high now and for the future while most don't (and this is a dynasty league). WELL, there were two so-called 'expert' owner's that went off saying Charles wasn't that good to the point that to appease this issue, the commish stated he would review all trades (though he hasn't stopped any since and I've made more since). So here we are finishing week 12 and both those owner's (the so-called experts) will have the worst record in this league and my team is tied for the best, with Charles leading the way (and getting better with each week). Ironically, one these two owner's actually made a trade offer to me for Charles.....I just laughed as I hit the reject button.....lol
Bottom line is all owner's have different value systems, so unless we know what each owner is thinking at the time of each trade, we need to give the benefit of the doubt.....
.....unless it's Trade 2 above, then that's appears to be fairly obvious (friends or non-friends)!