Answer:
A dying fish could show any number of signs. Some of the most common could be loss of color, loss of appetite, lethargy, etc. If any readily apparent signs of issues are present with your fish, your LFS should be able to interpret these symptoms and recommend a course of treatment that could possibly save the fish. Do not remove the fish from the tank for transport to show the LFS cause that will stress the fish and would further increase any distress the fish has possibly ending in death.