In all honesty, it is tough to sell art in today's competitive market. All of the search engines and social networks are giving preference to paid ads. That was always their plan.
Here, I have sold a few prints over the years. I have quit this site and recently came back. But it isn't just this site where selling art has become a greater challenge. It is the same on Esty, eBay and Amazon. It's no longer a given that if you have good work and promote it you will make consistent sales.
That's my experience and take.
For example, on this site, all of my work is buried so far back it is doubtful anyone will ever see it. Yet, the front pages are filled with duplicates and in some cases not the best representative work. Go figure. I know all the reasons, but none of them seem fair.
Also, facebook groups are fickle and will expel you at the drop of a hat, if it is perceived you are not playing by the rules, even if you think you are. Put another way: Online selling is no longer conducive for making a constant revenue stream for most artists, not all. Those who succeed have found a way to post enough links on fruitful sites and page. They also know how to work the system here.
Those secrets, of course, will never be shared. Can't blame them.