Depends on what the artists goals are. Some people like to paint and are happy that someone likes their work and is willing to give them 20 bucks so they can maintain supplies and paint some more.
No easy task making a living as a painter. Run the numbers whether you sell in galleries or sell on your own you have to be very prolific. Unless you one of the very few who get 50k a work.
Plus the more you produce and sell could lead to higher priced sales in the future from collectors. Understand that just because someone that can only pay 25 bucks for one of your works now doesn’t mean they can’t pay $250 in the future, as peoples income changes all the time.
I personally have sold well over 500 paintings over the years online maybe more. Many of them under 25 bucks. But I now have some of those collectors who have paid 10x that for a very similar work.
Its all about the goals the artist sets.
This also leads me to another point on selling ones work cheap. Its a good thing for the artist if people buy your works and try to resell them at a profit. You should want that, it only increases the value of the artists work.
I’ve seen some posts in the past where artist are mad because they sold a work for $25 online and the buyer resold it for $50.
So what!! This is literally the idea of constructing a work of art and selling it. When a collector purchases an artist work they want feel that there is value in the purchase. They are also building their net worth. They may decide to sell it down the road and make a profit if the artist work is selling for more. The artist has no claim to that profit.