No need to return it, I totally understand becoming attached and it's honestly unnecessary since mites are easily treated. I'd treat for mites (with Provent a Mite) as directed on the can, and never go into that shop again. I'd watch the supposed scale rot, and take out any substrate you use and replace with paper towels asap. If the scale rot looks mild you can always try Neosporin (without the pain killer...just the plain) once a day until he/she sheds. If it looks better after the shed then you know it was the problem and it was fixed. Without pictures of the belly there's no way to diagnose anything, so don't take my word for it. Can you post a nice close up clear shot of the area you suspect?
http://www.pro-products.com/index.ph...d=53&Itemid=59