What is fair compensation in NFL trades?

The NFL has not had many trades involving players, so I will show through a few examples the flaws in fair compensation for a player.

In the news of the Cleveland Browns, they just received wide receiver Jarvis Landry from the Miami Dolphins in exchange for a fourth-round pick and a seventh-round pick out of a seven-round draft, which according to NFL.com is April 26-28,2018. Landry, who lead the league in receptions last year in addition to making the pro bowl the last three years can be considered a number one wide receiver on many teams.  He is only 25 years old.  Now I would like to compare that trade to 2010 when the Denver Broncos traded wide receiver Brandon Marshall to the Dolphins for a second-round pick that year and a second-round pick in 2011.  Marshall was a very similar player regarding stats to Landry at that time.  Additionally, he had only made two pro bowls at the time to Landry’s three.  We do not know how Landry will perform in Cleveland but just on the surface two second-round picks are way more than a fourth and a seventh.    

Next, I would like to look at the legendary Herschel Walker trade.  Walker was a great running back for the Dallas Cowboys at the time, the problem? The team was not good.  In 1989 the Cowboys started 0-5.  The current coach and GM at the time, Jimmy Johnson wanted change.  He went to the Minnesota Vikings and ultimately getting 13 players/ draft picks for Walker and 4 draft picks.  One of the picks was used to draft Emmitt Smith who is a Hall of Famer.  Additionally, the Cowboys went on to win three super bowls in the 1990’s.  According to Fox Sports, Johnson wanted to prove that he could draft well, so even though the players they got from Minnesota were better than the current starters, Johnson wanted them benched. 

In conclusion, through these three trades, it is shown that trades in the NFL are not based on a certain guideline but rather the value the player is to the team.  Additionally, for how cheap the Browns got Landry, and how expensive the Vikings got Walker it is given that there is some persuasion going on behind the scenes, which makes me wonder, what makes a good GM vs a bad one?