The replacement part for the iPhone 4 rear panel has two thin, clear overlays on the inside surface--a larger one that runs the full length, and a small one that only covers the lens. These should be removed prior to installation. Also, the first rear panel replacement I got from iFixit was not an exact fit and would not easily "click" into place. They replaced it for free and the second one clicked right in.
Once they have, you'll be able to view a graph of their reputation gained over time.
Here's a preview of what the graph will look like:
No reputation gained yet.