The best way to judge if a trade is fair is to figure out how many fantasy points each player involved in the trade will score this season. Once you know that, it should be pretty easy to see who is getting the short end of the stick.
Small nitpick. No, actually, as I start to type more, large nitpick. That isn't a good way to evaluate a trade.You need to consider the entire roster and resulting starting lineups before and after, not the total points of the players traded. I can trade you a 300 point QB for a 180 point TE. It could be that trade will end up being a -30 points on the year for my team and a +30 for you... or it could end up being a +30 for me and a -30 for you, or it could end up that both of us improve by 30 points (which would make it a very even deal). It would depend entirely on what else changes in our starting lineup because of the trade. Even a straight adding up like you suggest of VBD value won't work. How good the starter that you're replacing, or how bad the backup you now may have to start, also play a role.
And that still doesn't take into account other things, like averting risk of injury, or an even bigger thing like the true market value of the players. If no one is wanting to trade away RBs, you are going to have to give up more for one than if there are 3 RB rich teams who are all looking to trade one to upgrade some other position.
To give a real life example, a few years back some of the owners in my league complained when I traded Duce Staley (originally an 8th round pick) for Jeff Garcia (originally a 2nd round pick) I told them, "Name a single team in the league that Garcia is an upgrade for at QB, who can afford to give up a better RB than Staley." There wasn't one. Staley was by far the best RB this team was going to be able to get for Garcia (who was his bench QB as his backup was Bledsoe who ended up #1 that year).
In short, he traded Garcia for the absolute most any team would give him. That's the definition of an owner having made the best trade for himself that he could.
That's part of the problem with how people evaluate trades. They try to judge them by what they think a nameless"someone" SHOULD be willing to give up, rather than judging it by what real owners actually ARE willing to give up. And it's one reason I won't play in a league that allows owners to cast vetoes.