Odd and random question. I bought an iPhone 4 off Craigslist. Though it's performing great, I have this sense that the display might not be the Retina. The reasons being, whenever I've looked at an iPhone 4 with my polarized sunglasses on, the display wasn't clear. This screen is. Also, from the side, it's completely viewable. Is there a way to see if I actually have a retina display or if it might have been changed? Thanks for any help.