Instead of building an MVP and then trying to sell it, there are people who suggest: 1-Think of an idea. 2-Make a simple landing page with a mockup or something. 3-Try to sell the product. And by selling the product I mean actually selling it (so people actually transferring you money). If you can achieve a given amount of sells in a given amount of time (important: set concrete goals with concrete timing), then you…
What you describe is smoke testing. However, taking money and not having a product is considered fraud in the US. The way you get around this is that on the final confirmation page where you would normally take payment details you instead say the product is on backorder but that the person can enter their email to be notified when it's available. That'll give you the stats you need without running afoul of the law or…
The point is that to actually validate a product idea, potential customers should actually pay, or show a real interest in paying, for that product. Otherwise, it's not validated.
Disclaimer: never tried, but it's a typical advice I read in this kind of posts.