Same thing with pickup volume, if you provide poor service you’ll lose customers.
In your case, a FedEx contractor, you will not lose any customers, they (the shippers) aren't your customers.
These shippers have made their individual service agreements with FedEx, you aren't a party to their agreement.
You answer to FedEx, wholly, totally, no one else. A third party to your business can put your business in a world of hurt.
Run a test,
provide poor service, after their initial call to you, find out exactly who they address their concerns to. Find out exactly which party to their deal will reprimand YOUR business.
Your business exists at the pleasure of FedEX not those you portray your customers to be.