In Chapter 11, we learn the following about Stan from the Daily Prophet:
"Stanley Shunpike, conductor on the popular Wizarding conveyance the Knight Bus, has been arrested on suspicion of Death Eater activity. Mr. Shunpike, 21, was taken into custody late last night after a raid on his Clapham home…" (11.30)
Harry, who knows Stan to be a good guy, loses even more faith in the Ministry when he learns this. He realizes that the Ministry arrested the innocent Stan simply to make the public think they're doing a good job capturing Death Eaters.