Schells is the name of the gambler in Mass Effect, whose tampering with some of the gambling machines got him kicked out of the nightclub Flux. The thing is, Schells was gathering data to simply create a cheating system, absolutely no harm there!
Mass Effect Schells: Where to Find the Gambler?
Once the player first gets to the nightclub and starts the assignment titled "Rita's Sister," the next time you enter Flux a brief cutscene plays showing Schells being thrown out due to his escapades.
Schells explains to the player that he is trying to perfect his new system that predicts the outcomes of one of the gambling games called Quasar. If the player originally denies Schells help, he will be at the entrance of Flux until you accept his assignment.
Different Choices for Schells the Gambler
Spoilers ahead if you don't want to know the three outcomes for the Schells assignment!
"RECORD THE DATA" - If the player chooses to assist Schells on his mission to game the Quasar machines, you must play Quasar until you win five times. The device Schells gives you will then alert saying sufficient data has been gathered. You can return the device to Schells for XP and a chunk of credits and no morality reward.
"LOSING THE DEVICE" - Doran, the owner and main cook of Flux is keeping an eye you. If the player gets too greedy with winning Quasar, on the seventh win Doran will confront you and confiscate Schells' rigging device. Doran goes as far as to take all the credits you earned from the seven Quasar wins you just partook in. Once the player breaks the bad news to Schells, the assignment ends with no credit, morality, or XP reward.
"GIVE THE DEVICE TO DORAN" - For the final option, the player can take the snitch route and go directly to Doran, telling him about Schell and his plan to rig the Quasar machines. The XP and credit that Doran gives you is the same amount you get if you were to bring the device to Schell after gambling in the first option. Furthermore, there is once again no morality rewards for this option.