As a longtime fantasy football commissioner -- I started my still-running "Doug Logan League" way back in 1993 -- I've always been an advocate that you should let your fantasy managers make whatever trades they want, so long as these deals fall within the parameters of fair play.
For example, if a handshake deal was struck between two members of your league during Week 4's Bengals game for Tyler Eifert but, before the appropriate clicks were made on ESPN.com to make the swap official, the manager getting the Cincinnati tight end chose to back out of the transaction, your decision as LM should depend on the full circumstances of the agreement.
Say the deal was agreed to in the first quarter, shortly after Eifert caught a TD pass from Andy Dalton. Well, then, the trade should stand. Just because Eifert suffered a catastrophic injury later in the contest, but before the proverbial ink on the deal was dry, doesn't mean anyone now has a valid reason to back out.
By the same token, if Eifert's original fantasy manager was watching that game and reached out to make the deal as the tight end was being carted off the field, in the hopes of rushing the transaction through on the strength of, "Hey, he even scored a touchdown today," before word of the incident got out? In that case, the shadiness of this move absolutely warrants a veto.
However, while deliberately concealing new information that impacts a player's value is definitely worthy of a flag for unsportsmanlike conduct, that doesn't mean it's your responsibility to do your potential trade partners' research for them.
With Drew Brees and New Orleans playing on Monday Night Football in Week 5, it could be forgiven if league managers with Saints in their lineups are not yet looking ahead to Week 6, when the team is on a bye. So, it might not be at the forefront of their mind when you, with Matthew Stafford as your backup quarterback, offer him up to someone with Brees as the sole QB on their roster.
Some might call this shady dealing, as well, since Stafford is also on a bye for Week 6 and, as such, is of no help to the Brees owner hoping to cover his off week. Still, that's not your job. If a fantasy manager isn't smart enough to notice these important details, it's on them. Of course, you also don't want a reputation of being "that guy," lest you find nobody wants to trade with you going forward, so tread carefully in situations like this.
However, there is indeed a very viable veteran move still at play here, and just because you don't have to do anyone's research for them, that doesn't mean you shouldn't. Go ahead and look at the rosters of your league mates and see which of them has not properly prepared for future bye-week replacement. OK, maybe there's enough left on your league's waiver wire to cover Brees, Alvin Kamara or Michael Thomas sitting out next Sunday. However, starting in Week 7, the number of teams on bye each week begins to multiply. The waiver well will start to run dry quickly, especially in leagues with 12-plus teams.
So, the earlier you can get in there and offer up a deal to someone who didn't notice on draft day that it was a bad idea to have all your options at one position coming from either the Green Bay Packers, Oakland Raiders, Pittsburgh Steelers or Seattle Seahawks, the more likely you are to get a deal done -- and, likely at a significant markup in value, especially if you're the one who did this fantasy manager a solid by alerting them to this dilemma they didn't even know they had in the first place.