What do you think?

Simple yet not. Just start talking to the guy (if you don't already) and continue to get more friendly with him (but not too much). If there is some sort of reaction from him which indicates even the slightest that he might like you, then your in the green light.

Just confront the guy that's all.

If there is a good enough reason to believe that she is lying, than don't do anything, but why would your BFFL lie to you for something like that? If you like the guy, just go talk to him. It could be about anything, but just don't ask him straight up if he likes you or not. If he does, he will respond positively when you approach him. You also should not make it too obvious that you like him when you talk to him for the first time.

It'd help to know why you think she's lying. Do you just think she's lying because you don't want to get your hopes up? If she's really one of your best friends, she probably wouldn't tell you a guy she knows you like likes you back if it weren't true. I bet she's telling the truth. But if you really aren't sure, I'd just come out and ask her why she thinks so, how she got that info. Or if there's someone else you're really close to that might know, you could casually ask them if they know anything about who he likes, and see if they say the same thing.

I would just confront the guy and ask him myself.

There is a reason that your BFFL is telling you someone likes you. I say that you should just ask him. Tell him that people have been telling you that he likes you. Ask him if its true. If your BFFL doesn't want you to tell him that she was the one who told you, then tell him that it was an anonymous person. I hope this works! Also, BFFLs shouldn't lie ;];].

Talk to him and she actually might be right.