Unfortunately, it's not likely that anything could have been done.
What you saw is typical damage due to poor acclimation. The shrimp likely had no hand in causing it. Keep in mind that while you may have acclimated the star properly to your tank, along the chain of custody there were several other opportunities for other people to acclimate it poorly to their holding systems. By the time the wounds start to show, the damage has already been done and there's no way to undo it.
If you want to try another Linckia make sure that the LFS holds it for a few weeks. A month is best if you can convince them to do that. If at that time it's still plump and doesn't have any discolored spots or wounds, it's probably safe to take home. Be sure to acclimate it carefully though, and make sure it goes in the 120, not the 55, otherwise it will likely starve down the road.