One problem is, artists just don't have the resources to continually follow up on this.
I went to a show recently my brother/sister in law who really wanted the print but the merch lines were nuts. It wasn't an over the top amazing print, nice clean design, simple (and over 3 nights, it was the same print with 3 different colorways), certainly not a flipper. I said I'd take care of it after the show, assumed I would be a bit more savvy to acquire it and felt I could get it on the band site or artist sale later.
Went to ebay and saw immediately, a slew of new accounts selling the image in a myriad of sizes.
As the artist isn't really in the poster scene (more a tattoo artist doing an occasional band print), I reached out and asked when they might sell their copies, we chatted back and forth a bit. When I let them know about all the ebay accounts stealing their image and reselling it, their response was:
"Thank you, yea it’s a battle that seems hard to win. I can either keep drawing and ignore it or pay for a legal team so I try to choose the former "