Doram That’s very theoretical, and I have no argument with the theory. In practice, however, I think it’s even simpler and I believe this is in fact what is actually happening in real life most of the time. I sometimes weigh things I buy. I do it to check the accuracy of my scales, not to see if sellers cheat me, because I believe they don’t. I can’t remember an occasion where I got less than the advertised weight, but I certainly got more than the advertised weight many many times.
The bigger and more advanced the manufacturer, the more chance they will be able to hit the mark and get the exact weight or very close to it. Smaller businesses (like a neighbourhood roastery) are more likely to overshoot the weight by more. Do they lose money over it? I believe not: if they know how to run a business, they factor it in and the consumer pays for it (as for everything else). So back to square one: the consumer pays the price for the product + for the cost of variations you describe, therefore it’s the sellers responsibility to make sure the consumer will get the advertised weight (or more, if the seller can’t guarantee this) - because the consumer paid for the extra costs incurred by that as well.
Now, if you tell me that the seller saves by not doing this and passes those savings to the consumer to offer a better deal, then that might change the equation, but I doubt I can be persuaded that many businesses do that.
I agree with almost all of that - most suppliers aren’t out to fidde us, and I’ve had the same experience …. under weight is pretty rare, a smidge over isn’t that rare. I also agree that many or most will go over by a small amount, the cost of which is generally so nominal that it doesn’t really matter whether it’s in the price or not.
Where we part company was in the characterisation of “making sure” that it’s “at least” the specified weight, and that “every buyer” gets that. They are absolutes - if you want to be certain every buyer, every bag, every time is at least that weight, the inference is it can NEVER, ever be less. There are so many ways that can happen, from the aforementioned dirt, coins, movement of the unit, unbalancing it right up to component failure and just the effect of time that the only way to make absolutely sure is a level of rigour in weight control so over-the-top that it just isn’t practical, and doesn’t happen.
I might attribute a different motivation to putting a little extra in, though, which is that in many circumstances it will be an offence to trade with the product being below the legally mandated level of tolerance, and they’re quite keen not to do that. Also, there are those random tests not only by Trading Standards but also by those 3rd party verifiers. The bulk of the time, if verifying that a scale is compliant I found that it wasn’t, I could and would find the issue, rectify it and re-verify the scale. Occasionally a problem was such that it needed a service engieer and/or part, and I’d decertify the scale, meaning trading on it was illegal and that could meant closing that checkout until the problem was sorted. Many stores had either a spare scale on standby out the back, or we could cannibalise their training room setup rather than take a checkout out of service because that, in busy times, could hit the bottom line and wasn’t a popular move.
Anyway, what’s not practical is that level of certainty that every single bag, every single time, is at least any specfied weight. But with scale accuracy and reliabiity (at least these days) being actually very good, they don’t really need to add extra because of the minimal, and non-material, error rate and level allowed.
It’s a statistical game, if you like. They can be x% sure that they are within +/- y grams, z% of the time. The occasional outlier? maybe. But rare. It’s being 100% sure every single time that isn’t practical. Or affordable.
Are there rogues out to fiddle us? Oh, hell yeah, but not in supermarkets and (IMHO) not in the bulk of small businesses. But an element, yeah. There’s also many ways of doing that, most of which don’t involve weighing.
