I actually think this is a good tactic. Basically you try to sell a product that doesn't exist to determine whether there's any demand. Off the top of my head

I actually think this is a good tactic. Basically you try to sell a product that doesn't exist to determine whether there's any demand. Off the top of my head I can think of at least 4 large ($50M+ acq. or valuation) teams that picked their products this way. It's pretty easy – build a well designed landing page describing the product, share it on HN/reddit/etc and gauge the response.