Let us begin with power. Power is a perception, it is an abstract idea which must be agreed upon by more than one. Without the agreement and relinquishment of power (from one party to the other) power cannot have an effect or indeed exist at all.
Perception of power is the worst. This is when a group or individual, believes they yield a power over another, without the other being a party to the agreement. In other words, you think you are the shit when in reality you are just shit.
This is the driving force in many customer-supplier relationships. The customer somehow perceives power over the supplier, they are paying for a service and so, they own the supplier.
The last mile provider always endures this perception of power. An individual is frustrated with the delays, holdups, unforeseen costs. Instead of having the backbone to address the providers in the chain who matter, they vent on the last mile provider.
Use your head. Correct mistakes at the appropriate level. Venting on the last mile provider will serve no purpose.