So, I deliver a couple of packages for Contreras at McCarran, the third package is supposed to go to a guy named Price amd there is a password. Price isn't there and the guy who is, Keller, dosn't know the password. I go back and tell Contreras this and he says Keller is undercover NCR and has to be killed. My character is a good guy, so I go back and tell Keller that Contreras is smuggling and wants him (Keller) dead. Keller asks why I'm helping and I say Contreras is a scumbag who needs to be caught. Keller tells me there isn't enough evidence, and that I should go talk to Boyd at McCarran, but when I talk to Boyd there are no new conversation topics, and when I go down to where Contreras was he is gone. I keep running into this kind of crap. I swear I remember Fallout 3 having a few bugs, but nothing on the level of New Vegas. It's like it wasn't play tested at all.

I had the same problem. I killed the ncr guy and then I went back to Contreras and it said that I got the ncr guy to cooperate, nothing about price.

I have no problem with that. I killed Keller when the option to kill up shows up in the conversation. I went back to Contreras and he gave me "The Machine" as a reward.