Testing before launch is how you find out what people will actually pay for while it is still cheap to change. A week of asking saves a season of building the wrong thing.

A test with real customers is worth more than any amount of planning, because the answer comes from behaviour rather than opinion.

You need a version good enough to show, not good enough to sell. A sample, a photo, a one page description, a single prototype. Polishing it first defeats the purpose.

You also need five to ten people you can ask honestly. People who have bought from you before give the most useful answers, because they have already proved they will part with money.