If there is one, then I'll check the sidebar there, read through some posts, search for a few keywords. Basically spend 15 minutes researching.
Reddit still has shills and astroturfs, but for a lot of niches they're often aggressively moderated out of the community.
To go along with your umbrella example:
Unfortunately /r/umbrellas isn't a thing, but I did find this thread[1]. Sprinkled throughout the comments are links to sites that seem to be on the up-and-up.
[1]https://www.reddit.com/r/BuyItForLife/comments/a4afrg/guys_d...