What? He couldn't "sense" Goku's Ki accurately? That's a really weak argument, guys. Beerus isn't one of Frieza's henchmen, he's the God of Destruction of DBZ Universe 7. He's not going to be fooled by Goku "not being powered up".
That method of deception was valid only if somebody was using a measuring device for measuring somebody's power level (for eg: a Scouter, or Dr. Gero's sensors). All people who have been shown to be able to sense Ki have not been fooled by the power level disguising trick. Granted, Beerus may not have accounted for a Ki amplification technique like Kaio-ken or Super Saiyan, but I'm pretty sure he was able to sense the entirety of the Ki possessed by Goku in his base form.
Off-topic: Now, most of you might be feeling underwhelmed by Goku's power progression throughout the series. You may be feeling: "What? He only became (less than) 50 times stronger by the end of the Buu saga?"
Yes, his BoG base power does seem rather low, but I assure you, it actually an incredible figure. Want to know why? Simple example: Perfect Cell was toying around with Full Power Super Saiyan Gohan. Yet Super Saiyan 2 Gohan absolutely stomped him. And that was with just a 2x power up. When you look at it that way, 50x is a pretty accurate figure, no?