Just about any camera with a good lens will do the trick. The problem is that most cameras today have cheesy little nothing lenses. So start by looking at the glass. Does the camera have a larger lens? I know that sounds simplistic, but it's the most important place to start.
After we get past the lens, you will need a camera that has a good digital processor. You'll need to read professional camera reviews to learn about the processor. A word of caution about reviews though: consumer reviews may not always spell out the actual facts - you may be hearing from grandma who just uses the camera to snap photos of the grandkids and isn't looking for critical quality like you are.
Don't get hung up on megapixels. Today's cameras generally come with 10 megapixels or greater. I've even had good results with a very old Canon G4 camera that has just 4 megapixels - but the lens and the processor was nearly "pro quality". In fact, we've used this camera for snapping some of the shots that you see on this website. It's been a good quick to grab and simple to shoot camera.
But in the end, a lot of it comes down to how you're using the camera. For indoor "before and after" photos TURN OFF THE FLASH. The flash will wash out the photo, and you won't see the contrast between the clean and dirty carpet. Rather than using flash, adjust the camera's white balance "WB" setting to match the type of lighting inside the building. It is generally not best to simply leave the WB setting on the Auto mode. In most cases you will be using a "fluorescent" setting inside commercial buildings.
Take your time to position the camera carefully in relation to the area you're photographing. And then hold the camera PERFECTLY STILL. It is best to set the camera on a ledge or a piece of furniture. Stabilizing the camera without flash is critical to get a good shot. Even the slightest breath of a jiggle can create blur in your picture. And you won't usually notice the blur in the tiny viewer on the camera. You will only see the blur when you get it back to your computer.
For what it's worth, this week that old Canon G4 that I mentioned above dropped dead on us. And we needed to get another camera to replace it. We ended up getting a Nikon L110. It is a very good camera for a consumer grade camera. (My nice camera is a Nikon D90, and I've still got a bag of old Nikon lenses that date back to the 1980's.) Here's a look at the camera we just purchased. I think it would do well for what you need it for...
http://imaging.nikon.com/products/imaging/lineup/digitalcamera/coolpix/life/l110/index.htm
Hope this was helpful to you.
Rick Gelinas