Recommendation

What Miss Aquarius℠ may look at when she suggests a tip — and what she must never see.

What she reads

The item, and the shop's own prices

Always

Cost basis, if the shop offers one

Never shown to a customer

Comparable items in the region

Calibration, after you are already at a shop

How people actually deviate

In aggregate, never per person

Shape of the suggestion

Default suggestion 12% of the item

Quick amounts offered 3

Skip always available yes · not a setting

Reasons shown with every suggestion yes · not a setting

An anchor, not a price. Deviating in either direction is signal she learns from — and black-box pricing would corrode the trust the whole arrangement runs on.

What she must never see, and it is not a toggle

— Who the customer is. She never needs an identity to suggest a tip.

— What this customer tipped before, or can afford.

— A per-shop dial. One function, published, the same for everyone.

— Anything that would raise a suggestion because a shop paid.

Personalised pricing is the same machine as ranked discovery, pointed at a wallet instead of a slate. This is open problem #9, and the honest state of it is: these are the constraints, not yet the answer.