Most companies we meet have their price list in order. Even so, net margin differs sharply between customers who look identical on paper. The difference arises in everything that happens after the list price: discounts, freight, add-ons, campaigns and old agreements nobody has touched in years.
The first sign is that you cannot explain the spread. If two customers with the same volume and the same product mix land on different net margins, the difference should have a commercial justification. If it does not, it is leakage.
The second sign is discounting without boundaries. When the mandate is unclear, the price ends up where the negotiation ends rather than where the value is.
The third sign is follow-up at aggregate level. Averages almost always hide the deals that drag the result down. Only when the analysis goes down to order-line level does the pattern become visible.