A customer's RFM score looks wrong

RFM scores are relative to your own store, not absolute, and this is the single biggest source of surprise. Each customer is ranked against the rest of your customer base and placed in a fifth of the distribution, so the same person can score differently in two different stores, and your scores shift as your customer base changes.

Two consequences follow:

• A high spender can score below five. If your store has many higher spenders, a customer spending well in absolute terms still sits outside the top fifth. Nothing is broken; they are being compared against your best customers, not against a fixed threshold.
• Scores move without the customer doing anything. Adding a wave of new customers, or a seasonal spike, redraws the boundaries for everyone. Compare a customer against your current distribution, not against the score they had last quarter.