Below is the link to the subject. It is an important part of the game as a bad trade is not only bad for the team that made it, but also for the rest of the league other than the team who got the better of the deal.
The primary rule is do not base your trade on the trade meter values and/or Ai player default ratings.
The older a player gets, the less his value should be. Dont trade a first or second round pick for a WR or RB that is 8 yrs or older, no matter what his rating is. The 9 yr mark is a major decline point for players who are speed oriented, WR, RB, DB. DL can go 12 & 13 and still be effective, same for OL & QB. LBs are iffy, some can keep their elite level ability longer than others.
Here is the link to the thread ..............
https://dfl.myfootballnow.com/forums/1/625?page=1#1346