A complaint lands in a queue, in front of a person with a script and limited authority. Knowing what that person can and cannot do changes how you write it.
A large company's standard agreement is written to protect the large company. Most of it is negotiable, and knowing which parts to push on is the skill.
A probationary period that nobody manages is just ninety days of hoping. It is meant to be a structure with dates on it, and it runs in two directions.
The last quarter is when the people who owe you money start managing their cash instead of yours. Here is the order to work through when an invoice slips.