Another reason to buy your camera from an authorized dealer is the all-too-common issue of stuck pixels (see the purple dot at right; also known as “hot” or “dead” pixels). With the extremely high pixel-count CMOS sensors (and massive sensor sizes) of current DSLRs, you will almost certainly get a camera that ships with a few hot pixels; video camera users accustomed to CCD-based imagers may not be ready for this. For pro DSLRs that ship with 20 million pixels, several stuck pixels are well within a manufacturer’s tolerated specs, and pro photo applications like Lightroom or Aperture often detect and fix stuck pixels automatically when you import still photos. However, there is no such fix for video, and while one stuck pixel out of 20 million unmoving pixels isn’t very noticeable on a still photo, one stuck pixel out of two million moving pixels is often noticeable (DSLRs record video in a reduced-resolution mode; 1080p is just shy of 2 million pixels). It’s not entirely necessary to test for stuck pixels in still mode with your new camera — you’ll drive yourself crazy thinking about your “defective” camera (if you really want to geek out, though, they have programs you can use to run tests).
However, you should absolutely enter a low-light setting, crank up the ISO, and pan across a plain wall in movie mode to see if you have any persistent dots. My first 5D had 16 stuck pixels in still mode and 1 on video, so I exchanged it (my second fared better, with 7 stuck/hot pixels in still mode, but again a sole offender in video mode, for which I’m planning on having it serviced). The hot pixel issue alone is a good reason to buy from an authorized dealer with a decent return policy, as every DSLR is like a box of chocolates. Except these days a box of chocolates is not, in fact, like a box of chocolates: there are pictures on the outside of the box and you usually know exactly what you’re going to get.
If you don’t detect a dead pixel until you’ve already shot your footage, all is not lost. I wrote a post on the very subject of removing dead pixels using Final Cut, After Effects, or Vegas: How to remove stuck pixels from video footage.