If you are the sort of person who enjoys the making side of things, and aren't naturally gifted at selling, this can be a trap. I've seen so many solo founders try to validate a product by selling before building, only to get talked into different features and use cases until they're stuck building some bloated mess of a service. Not super enjoyable.
That said, if selling is your strong suit and you have the discipline to sell a product idea without deviating from your product idea to chase sales, then selling as a validation tool is fantastic.
This is a provocation/question - not a statement of fact btw!
Not saying that this never happens, but it is extremely rare and closer to gambling than to running a company.