What a +EV scanner is actually doing

A scanner is not magic and it is not always right. Knowing exactly what it computes is what lets you tell its good flags from its bad ones.

A positive-EV scanner looks like magic and is not. It runs one calculation across thousands of prices very quickly. Knowing exactly which calculation is what lets you tell its good flags from its bad ones — and it does produce bad ones.

The four steps, every time

Collect the same market at every book. The same game, the same line, the same period. This step is where most errors are born.
Pick a reference. Usually a sharp book, or a consensus of several.
De-vig the reference to get a fair probability.
Compare every other book's price against it. Anything paying more than fair is flagged, with the gap reported as an edge.

That is the whole algorithm. Everything else a tool does — filtering, sorting, alerting — is presentation on top of those four steps.

This means a scanner is not finding mispriced games. It is finding books that disagree with each other, and assuming the sharper one is right.

What an edge usually is

When the assumption holds, a flagged bet is a stale line — a slower book that has not yet moved to where the market went. That is a genuine, if short-lived, opportunity, and it is what most real +EV flags are.

When the assumption fails, the flag is an artefact. The four common failures:

Why a large edge is usually not an edge
Failure	How it looks	How to check
Not the same market	A huge edge on a prop	Confirm the period, the stat and the exact line
Stale data on our side	An edge that persists for hours	A real one closes in minutes
The soft book is right	A single book badly off, alone	One book disagreeing with all others is often correct
News not yet priced	A big edge minutes after an injury	Check whether anything just happened

The checks worth running

Is the reference book's number current? A fair line built from a stale reference is worthless.
Is the edge plausible? Under 3% on a main line is normal. Over 8% on a main line is almost always an error.
Would the book take a real bet? A price you can stake $5 into is not the same opportunity as one you can stake $500 into.
Did the line already move? If the reference has moved and the flagged book has now matched it, the edge is historical.

A scanner cannot tell you what it does not price

Every tool, this one included, only sees the books and markets it collects. An edge against a three-book consensus is a much weaker claim than an edge against twelve. Any tool that will not show you what it measured against is asking for trust it has not earned.

What it costs to use one

Betting flagged prices consistently is the fastest way to get limited at a recreational book, because taking a number seconds before it moves is the clearest possible signal of an informed account. That is not a reason to avoid it — it is a reason to expect it and to spread action across several books.

The honest summary: a scanner turns a research problem into a speed problem. It does not remove the variance, it does not guarantee the reference is right, and it never makes a losing month impossible.

Every flagged bet shows the fair price it was measured against, not just the edge. See the scanner's working.