Keith's Caravan Charade

Keith's Caravan Charade is an unmarked quest in Fallout: New Vegas.

Detailed walkthrough
Offer Captain Parker a helping hand. He will ask you to find evidence that Keith is involved in chem dealing and crooked gambling, adding the note "Investigate Keith's gambling and drug operations" to your Pip-Boy. Locate Keith's deck of marked cards in a desk in the southwest corner of Aerotech suite 200.

You can discuss the deck directly with Keith by passing a Barter check of 45, which will allow you to purchase jet from him, and a Speech check of 60, in which he lets you in on his 'system' for winning at caravan. This does not affect the outcome of the quest.

Return to Captain Parker with your findings, he will reward you with 150 caps and you will be given the option of assisting him in arresting Keith for an extra reward. The Captain will then enter Aerotech Suite 200 and confront Keith, who taunts Parker with slights about his ex-wife. Enraged, Captain Parker murders Keith. Talking to Captain Parker afterward will net you an additional 100 caps.

Bugs

 * Rex may turn hostile against the junkies, causing Keith to flee and ending the dialogue between Keith and Captain Parker. This may be related to the bug that triggers seemingly random attacks on Rex. If this bug affects you, reload from an earlier save and take all of the food and water items out of Rex's inventory.
 * Captain Parker may disappear from the game when entering Aerotech Suite 200 to arrest Keith. This can be fixed by reloading a saved game.
 * If Captain Parkers' quest The Coyotes is in progress and has not been completed, you may not be able to show him Keiths' marked cards. The only dialogue option is to mention that you're still looking for evidence.
 * Sometimes when Captain Parker goes to confront Keith about the marked cards, Captain parker will not initiate conversation with Keith but leave as if he did. This makes it impossible to complete any of the unmarked quest. Captain Parker's dialogue will stay as if you never showed him any evidence of Keith's wrongdoing but will never give you the option to show the evidence.
 * After completing the quest and Captain Parker kills Keith and gives you a reward, you might get the option to speak to Captain Parker about Keith again. Parker will give you the information on Keith again as if Keith were still alive. Needless to say, since Keith is dead you cannot repeat the quest.
 * Captain Parker might shoot Keith again after getting the extra caps for helping confront Keith. If this occurs you can talk to Captain Parker repeatedly and say goodbye to watch him continue to shoot the dead Keith.