To be clear, no big team is saint.
In all these cases whether it involves Madrid, Barcelona, ManU, Bayern, Liverpool, etc the referee tends to favor the big team when facing smaller ones.
Typically the distribution of decisions hovers around 60-40 in favor of the big teams but it's not because they were paid by them.
Unfortunately that is the nature of the sport nowadays compared to 90s.
In basketball (at least in Europe because i've no idea whats happening in the NBA) it's even worse.