People definitely do that, but most of the time it's DIY. Some reputation/brand SEO agencies offer it as part of “forum seeding” or “community marketing”, but it's usually expensive and not always done properly.
On forums like BHW, Reddit, or niche communities, a lot of brands seed discussions like “Best tools for X” and then participate with different accounts to recommend themselves. The key is making it look natural — mixing real competitors, different opinions, and not over-promoting.
If you overdo the self-praise or post from fresh accounts, it becomes obvious pretty quickly. Aged accounts, normal posting history, and balanced recommendations usually work better.
Personally I see it more as brand positioning + discussion seeding, not just straight promotion.