Cigarette Smoking Man: Secure the station. I want everybody else down below. If you're not armed, arm yourselves! We may have a breach.
Special Agent Dana Scully: Mulder, I can't tell you what killed this man. I'm not sure anybody else could claim to either.
Special Agent Fox Mulder: Scully, you gotta see this. Scully.
Special Agent Fox Mulder: Hey! You told me you had answers.
Alvin Kurtzweil, MD: Yeah. Well, I don't have 'em all.
Special Agent Fox Mulder: What do you want? Coke, Pepsi, saline IV?
Special Agent Dana Scully: I have to be in Washington, D.C. in 11 hours for a hearing, the outcome of which might affect one of the biggest decisions of my life and here I am in the middle of nowhere, Texas, chasing phantom tanker trucks.
Special Agent Fox Mulder: I just got chased through Texas by two black helicopters.
Alvin Kurtzweil, MD: And why do you think it is you're standing here talking to me? These people don't make mistakes.
Special Agent Dana Scully: Mulder what are you doing?
Special Agent Fox Mulder: Something's wrong.
Special Agent Dana Scully: Mulder.
Special Agent Fox Mulder: Something's not right.
Special Agent Dana Scully: Mulder get in the car! THERE'S no time.
Special Agent Dana Scully: Any thoughts as to why anybody would be growing corn in the middle of the desert?
Special Agent Fox Mulder: Those could be giant Jiffy-Pop poppers.
Well-Manicured Man: Trust no-one, Mr. Mulder.
Special Agent Dana Scully: Are you drunk, Mulder?
Special Agent Fox Mulder: I, I was until about 20 minutes ago, yeah.
Special Agent Dana Scully: Was that before or after you decided to come here?
Special Agent Fox Mulder: What exactly are you implying?
Special Agent Fox Mulder: After what you saw last night, after all you've seen, you can just walk away?
Special Agent Dana Scully: I have. I did. It's done.
Assistant Director Walter Skinner: Agent Mulder, you and I both know that if it looks bad, it's bad for the FBI. Blame has to be assigned somewhere.
Chosen answer: If they had put an "Out of Order" sign, or left it unilluminated, someone in charge might try to have it fixed or replaced, or could have checked to see if it's plugged in, etc. By leaving it illuminated, it doesn't look out of place and simply not taking money wouldn't arouse too much suspicion. In my own life, when I've come across a seemingly working vending machine that won't take my money or dispense drinks (but gives my money back), I just find another one instead of calling someone or reporting it. But yes, it is very convenient to the plot that Mulder just happens to try and use this particular machine.