Some prices can move and some cannot, and sellers know which

What follows is an argument about how sensitive demand is to price, and about where the received version of it stops being true.

The question behind every price change

Before moving a price, a seller is really asking how many buyers walk away for each step upward, and whether the remaining margin covers the loss. If demand barely moves, a rise adds money almost directly to the bottom line and the seller has every reason to take it.

If demand falls sharply, the same rise destroys more revenue than it creates and the price stays exactly where it is. This single question explains why some things on one shelf drift upward for years while others sit unchanged for just as long. It is not a judgement about what any item is worth; it is a measurement of how buyers behave when the number changes.

What makes buyers insensitive

Demand tends to hold up when there is no close substitute, because the buyer has nowhere obvious to go when the price moves. It also holds up when the purchase is urgent, since somebody with a broken essential is comparing against going without rather than against a rival. Items that take a very small share of a household budget attract little scrutiny, which is why small and frequent purchases absorb increases quietly.

Habit and loyalty do similar work, because a buyer who has stopped comparing has effectively stopped responding to price at all. Anything bought as a gift or for an occasion tends to be judged against the occasion rather than against the going rate for the item.

What makes buyers sensitive

Where near-identical alternatives sit side by side, a small difference in price moves a surprisingly large share of the sales between them. Planned purchases are more sensitive than urgent ones, because time allows comparison and comparison is what turns a price into a decision. Large purchases attract more effort per unit of money saved, so a rise on something expensive is scrutinised far more closely than the same rise on something cheap.

The number underneath says something else: categories where a reference price is widely known are unusually sensitive, since every buyer arrives already carrying a number to judge against. Anything that can be postponed indefinitely is sensitive almost by definition, because waiting is always an available substitute for buying.

How sellers find out

Large sellers learn sensitivity by changing prices in some places and not in others and then watching what happens to volume. Online the same learning happens faster and at finer resolution, because every price shown can be attached to whatever followed it. Promotions serve this purpose as well as a sales one, since a temporary cut measures how much extra volume a lower price actually buys.

At the till, the result is not a guess but a working estimate that gets updated whenever the underlying behaviour shifts.

Smaller sellers rarely have that data, so they tend to follow whatever the larger players have already established for the category.

Why this reshapes a whole range

A range usually contains items priced for sensitivity and items priced for margin, and they are almost never the same items. The sensitive lines are held low because their prices are what shoppers use to judge whether a shop is expensive overall. The insensitive lines carry the margin, which is why accessories, refills and add-ons around a well-known product often feel disproportionately dear.

Across a sale weekend, this is why comparing one shop against another on a single item tells you almost nothing useful about either of them. The comparison only becomes meaningful across a basket that resembles what you actually buy rather than what is easiest to check.

Consumer protection rules are national, and what is unlawful in one market is routine in another.

Using the idea as a shopper

Ask honestly whether you are a sensitive buyer for a given item, because if you are not, no amount of searching will help you very much. Where a close substitute exists and you would genuinely accept it, you hold real leverage and the price you pay should reflect that.

Run the arithmetic and where nothing substitutes and the need is urgent, the useful move is to shorten the list of things that can ever become urgent. Keeping a small stock of the essentials that break at the worst moment converts an urgent purchase back into a planned one. That conversion changes your own sensitivity, which is the only side of the whole equation you actually control.

The takeaway

Work out whether you are a sensitive buyer for a given item, because that answer decides whether searching is worth the effort.

The cheapest purchase is still the one you did not make.