The commonest failure in the category, and the easiest to fix.
What happened
A customer's container was placed on the scale, filled, and the reading was charged. That reading includes the container, and net weight excludes it by definition.
Why it happens
Because it is the obvious way to run a counter and nobody told the person working it otherwise. This is a training failure rather than a dishonest one, which is why it is so common.
The recorded tare went stale
A container re-weighed after a year with a new lid and a dried residue is heavier than the number on file. The customer pays the difference every visit.
The lid was in the tare sometimes
Weighed off for the tare, left on for the fill. A systematic overcharge that nobody notices because each one is small.
The scale was not zeroed
Which is the simplest version and the one a weights and measures inspector checks first.
The price was per jar
Which defeats the comparability requirement: a customer cannot compare a price per jar to the supermarket's price per fluid ounce. The method of sale has to let them make that comparison.
The method was mixed without being labelled
Shampoo by volume, oats by weight, one receipt, no units. Both lawful, and the receipt made neither checkable.
The delivery route was treated like the counter
A buyer who did not witness the measurement is the situation the bulk sale section describes, and the ticket requirement applies there even though it does not at the counter.
Nobody asked the state
The model law is not the law. A shop that opened without finding out which edition its state adopted is relying on a document that may not apply.
The fix is one card by the scale
Zero, tare, fill, subtract, price per unit. Five steps, written down, and everything on this page is handled.
References
NIST Handbook 130, 2023, Uniform Weights and Measures Law. Section 1.2: "The term 'weight' as used in connection with any commodity or service means net weight. When a commodity is sold by drained weight, the term means net drained weight." Section 1.8 defines net mass or net weight as "the weight of a commodity excluding any materials, substances, or items not considered to be part of the commodity. Materials, substances, or items not considered to be part of the commodity include, but are not limited to, containers, conveyances, bags, wrappers, packaging materials, labels, individual piece coverings, decorative accompaniments, and coupons, except that, depending on the type of service rendered, packaging materials may be considered to be part of the service."
nist.govNIST Handbook 130, 2023, Uniform Weights and Measures Law, Section 16, Method of Sale: "Except as otherwise provided by the Director or by firmly established trade custom and practice, (a) commodities in liquid form shall be sold by liquid measure or by weight; and (b) commodities not in liquid form shall be sold by weight, by measure, or by count. The method of sale shall provide accurate and adequate quantity information that permits the buyer to make price and quantity comparisons." Section 17, Sale from Bulk, applies its delivery-ticket requirement to "all bulk sales in which the buyer and seller are not both present to witness the measurement", to bulk heating fuel deliveries, and to other bulk sales specified by the director.
nist.govNIST Handbook 130 is a compilation of MODEL laws and regulations, not federal law. In NIST's own description they "are adopted in various forms by many state, local, and some federal weights and measures authorities. Some authorities adopt the current versions as written; some use them as the basis of adoption, but from an earlier year; some use them as a guideline only; some elect to use their own laws or regulations; and some have no corresponding law or regulation." The binding text is the one your state adopted.
nist.gov 