How do I know if my digital product idea will sell?
Updated
Look for people already asking
Validate an idea before building it by checking three things: are people already asking for it in public, does somebody already sell a version, and will anyone pay you today. Existing competitors are good news. Money is the only honest answer, so take a pre-order if you can.
Search the exact phrase a buyer would type and read the threads where people describe the problem.
Check that somebody already sells it
Existing competitors are good news. It proves people pay. An empty market usually means nobody wants it.
Read the one-star and three-star reviews of the products that exist. Those reviews are your product brief.
Sell it before you build it
Describe the product to ten people who have the problem and ask if they would buy it. Watch for hedging — "sounds useful" means no.
Better still, take pre-orders for a small version. Money is the only honest answer.
Set a stopping rule
Decide up front: if fewer than three people say yes, drop it and try the next idea.
Most ideas fail this test. That is the point — failing here costs an afternoon rather than a month.