N/A Kalibrgun Cricket not indexing

I have a .25 Cricket that has been as dependable as one could wish an airgun to be. With three .25 cal airguns I decided to sell one. Took the gun to a guy that sells airguns. Showed him how it worked, and shot half of a magazine with him. It worked and shot as it always has. I left the Cricket with the guy and he called saying the gun does not work. I got the gun back and it will not index. Does anyone have any input as to why this gun will not index the next pellet?