How does buying goods from outside prison work?

Question

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:

1. How does Red pay the guards?
2. How do the prisoners pay Red? It seems that all the interesting things they have in the prison are from Red anyway
3. 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
4. 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?

Answer 1

While multi-questions usually aren't allowed, I think I can answer all of these after having spent some time in prison:

1. Red pays the guards from the money given to him by the prisoners. Likely in a very secure environment like one of the workshops.

2. The prisoners pay Red from their bank accounts. Prisoners work and they get paid for that work, plus their families can add funds from outside prison.

3. This is so commonplace that not every warden can stop every transaction. In this case, he may have turned a blind eye if he knew it was Red doing it, and if that "contraband" wasn't anything serious.

4. Guards have expenses, and guards' pay isn't the greatest in the world. If they can make a couple hundred here and there on the side, why wouldn't they?