I started a buy/sell Facebook group a few years ago and have grown it to 28K centered around a specific locality in NC with a population of 32K. While I don't use it to market my handyman biz, I do use it to market another business that I own. The banner image for the group is an Ad for that business, and it alone generates leads. However, I believe its real value is in building brand recognition, equity, and showcasing our USP. When we get referrals from this area, they always know who we are and our value proposition. Makes the sales process MUCH easier.
Several businesses post in this group on a hyper frequent basis, 2-4 times a week. I've spoken with their owners, and they all agree that the group generates consistent leads/customers. So it works, but the key is consistency. You have to remember that posting frequently isn't necessarily about building brand equity...it's about advertising to a potential customer at the very moment they need your service. You never know when that is, so you have to do it all the time.
I would say that running one of these groups takes a tremendous amount of time. I was lucky to find locals to this area (frequent posters) who I invited to be admins. They now handle all of the admin tasks, and they feel like the Sheriffs of the group.
***My method for accomplishing the question asked***
Hire a VA (https://www.onlinejobs.ph/) pay them $200/mo
Purchase a VPN for them so their IP is in the US
Have them find relevant groups and post into those groups daily.
Have them comment on other users' posts that are relevant to your business.