The quietest of the four mechanisms, because there is no moment at which anything changed and no customer will ever describe it to you.
How the floor moves
A business establishes a standard that is genuinely good: it responds within a day, it is transparent about pricing, it makes starting easy. Competitors match it. Then adjacent industries raise the bar in ways that carry over, because customers do not compartmentalise their expectations by sector.
Nothing the business does gets worse. It stops being distinctive, then stops being sufficient, and neither transition is announced.
Why customers never say
Because they do not experience it as a decline. They experience it as this option being slightly more effort than another one, which is not a complaint, it is a preference. And preferences do not produce feedback, they produce a different choice.
This is the mechanism most responsible for the gap between customer satisfaction scores and market share.
The four places it usually shows up
Response time. The expectation has compressed steadily and continues to.
Transparency. What a business publishes about how it works, what it costs, and what it will not do.
Ease of starting. The number of steps between deciding and beginning.
Risk borne by the customer. Guarantees, trial arrangements, and exit terms. What was once generous becomes normal.
Why it is hard to argue about internally
Because everyone defending the current standard is telling the truth. It was good, it is still the same, and the metrics that measure it have not moved. The change happened outside the business, and nothing inside the business is instrumented to see outside.
The only reliable detection method
Compare against the best experience your customers have anywhere, not against your competitors. Competitors are subject to the same drift and comparing to them produces a comfortable answer. Customers are comparing you to whatever they used most recently, which is frequently not in your industry at all.