I Am Always Shocked When Someone Says They Find Me Attractive

I never know what to say when someone says that they find me attractive. Granted, I never know what to say to any kind of compliment I may get, but compliments on my appearance surprise me more than most other compliments. I'm not going to say that I'm this ugly, hideous person, but that being said, I also don't have any striking features, nothing that really stands out from the rest of the guys out there. I've got just an average looking face, I've got height (6'3), but I only weigh about 150 pounds, so that height is paired with a skinny, pathetic looking fr<x>ame, which makes my tall height look bad. (And please don't tell me to eat more, work out, ect, because I do, and guess what, it does little to help). So because of my lack of "striking features", and my average at best appearance, every time a girl says that I'm attractive, or even appears to hit on me. I'm left asking myself: "Is she just screwing with me?" "Is she just saying that because she feels sorry for me?" "Does she have low standards?" Or, "How much has she had to drink tonight?"