This girl complimented me but im not sure if its genuine or not?

If you've been getting it from other people as well then they probably mean it. Now, if they gave you a compliment that you knew wasn't true at all then you can doubt the sincerity of it. For instance, if your hair is frizzy, dry, and damaged, and someone said your hair looks nice, and you know darn well it doesn't, then they're just being sarcastic you know whats....