Then how did the YouTuber or course creator originally hear about the product? Unless a technology is already well known from other marketing channels, it's unlikely that unaffiliated people will just magically know about a new product.
Are you really so unimaginative that you’re going to follow the trail and at every point say “but surely THIS is where the marketing occurs!” without considering alternatives?
probably youtube or a course of some variety. the only times I ever gain anything from advertising is adverts for new series of tv shows