Most procurement guides tell you to "consolidate volumes" and "build long-term relationships" to get better pricing. That's true but vague. Here's what has actually worked for us:
Payment terms as leverage. Offering 30-day early payment instead of 90-day net in exchange for a 2-3% price reduction. Suppliers with cash flow pressure will take this deal every time.
Transparent cost breakdown requests. Ask the supplier to break down their price: raw material, labor, packaging, freight, margin. This shifts the conversation from "give me a discount" to "let's find where the cost can come down." Most suppliers hate it, which means it works.
Multi-year volume commitment. Even a letter of intent for 2-year volume with quarterly review gives suppliers enough certainty to reduce margin.
Competitive pressure without fake RFQs. Running a real RFQ process every 2 years keeps suppliers honest. Don't send fake RFQs just to pressure your current supplier — it damages trust and word travels fast in small industries.
What's worked for you that isn't obvious?

