Most on-chain risk is a matter of degree. Depth is thin, the round trip is costly, the pool is decaying — all bad, all measurable, all survivable with correct sizing. This one is categorical: the token permits buying and prevents selling.
How it works
A token is a contract, and the contract defines what a transfer does. Nothing requires that logic to be symmetric. A contract can permit purchases while causing sales to fail, or allow them only from selected addresses, or apply a fee on exit large enough to make selling pointless.
What makes it effective is that everything upstream looks correct. There is a pool, there is depth, there is turnover, and the chart rises — because buying works perfectly and nothing else is being tested. Every liquidity metric described elsewhere in this series will read as healthy, because each one measures the pool, and the pool is fine. The restriction is in the token.
Why this belongs beside depth analysis rather than inside it
Because it is not a smaller version of a liquidity problem, and treating it as one gives false comfort. Depth and volume both measure the pool. Concentration measures the holders. None of them read the transfer logic, so none of them can see this.
A trader who has correctly learned to check depth before sizing has not, by doing so, checked whether a sale is permitted at all. Those are separate questions and only one of them is answered by market data.
The adjacent version that is legal and common
Not every asymmetric contract is fraud. Plenty of legitimate tokens carry transfer taxes, trading restrictions during a launch window, or blacklist functions intended for compliance. The mechanism is the same; the intent is not.
Which is precisely why the honest framing is not “spot the scam” but know what the contract permits before you need it to permit something. The moment you want to sell is the worst possible moment to discover the answer.
What actually protects you
Verify the contract address against the project’s own published source rather than a search result — a token wearing a familiar ticker is not the familiar token, which is the whole argument in a ticker is not a token. Prefer tokens with a history of completed round trips rather than a history of purchases. And treat a rising chart on a token nobody has successfully exited as the least reassuring pattern on-chain, not the most.