This Roman call for caution has echoed over the millennia, and is as relevant today as it was on the day it was first uttered.
It is still an integral part of our law and commerce, carrying a warning to all those entrusted with committing an organisation's money. And this warning is specifically aimed at the buyer.
Somewhat more recently, but in the same vein, Chester Karrass famously warned that one must never assume that you are getting the deal you deserve, and that one should challenge all assumptions.
The difference between good and poor procurement can easily be 10% of the value of spend on procured materiel and services. Assuming spend at 35% of total cost, and a 20% margin, it implies that additional profit of 14% (or more) may be forgone.
Perhaps a bit of introspection is in order?