Validating an idea isn't just getting a yes or no. You need to understand what the person's problem is, how much that problem costs them, what solutions they have tried before, what problems did they have with those solutions, etc.
And then you have to size the market. How many other people have that problem? How do you reach those people?
Someone telling OP "interesting, I would buy it" might even be worse than not trying selling it at all, as it might fool OP into working even harder for nothing in the end.