A market stall earns a regular customer through ordinary exchanges remembered accurately.

Loyalty is mostly made of being remembered correctly. Not flattery, not a scheme with points, but somebody recalling that you take the small loaf, that you were away for a fortnight, that your mother was ill last month. Accuracy is the compliment: it means the interaction registered as involving a person rather than a transaction.

Try remembering one true detail about someone you deal with regularly and using it next time, without making a display of it. Write it down if your memory is unreliable. Being known slightly is one of the few pleasures that costs the giver almost nothing.