In Shawshank Redemption Andy buys several things from Red, when his cell was inspected the warden found some of the things but didn't care much. I get the basics on how this works: Red bribed some of the guards in order to buy things outside the prison and sell it to Red
Many questions arise:
How does Red pay the guards?
How do the prisoners pay Red? It seems that all the interesting things they have in the prison are from Red anyway
Why doesn't the warden take enough measurements to prevent? This of course is a security issue (which ultimately allowed Andy to escape), so I reckon the warden takes any measure possible to prevent this
Why do the guards help the prisoners buying goods from outside? The warden is so corrupt and brutal that any sane guard who doesn't play the warden's game would immediately quit and work somewhere else?