Specialized, from my experience, tends to run wide and a little big. Granted, I have a narrow heel and it slips in pretty much every shoe out there (street and cycling). but my heel slips badly in my Specialized shoes, to the point where I can feel it slipping with each pedal stroke. I'm not sure how "normal" heel slip should be, and I'm somewhat suspicious of it being an attempt to close the sale.

If you have a narrow heel, consider Louis Garneau (they didn't work for me, but they might for you), Sidi or Mavic, depending on how narrow your heel is relative to the rest of your foot.