1. Recent momentum
Compare demand over the last several weeks against the weeks before that. A meaningful drop — not a single bad week, but a sustained double-digit percentage decline — is the first sign something has actually shifted, rather than normal week-to-week noise.
2. Long-term direction
Zoom out to the full trend line over a year or more. A single dip can happen inside an otherwise rising trend. What matters is the overall slope: is interest meaningfully lower now than it was a year ago, or is a short-term dip sitting inside a longer uptrend?
3. Does it repeat every year?
This is the one sellers skip, and it’s the one that matters most. If a dip shows up at roughly the same time every year, for multiple years, and recovers by roughly the same amount each time — that’s seasonality, not decline. A drop that doesn’t recur on a yearly pattern, and doesn’t recover, is the real thing.