Real estate photography is typically a high volume and low margin business. You do a lot of shoots for not a lot of money for each shoot, so you have to learn to shoot efficiently and quickly in order to make your work profitable.
Sky replacements generally take too long for all but the higher-end real estate photo shoots because they are time consuming; however, I've worked on a technique that allows me to do any sky replacement in less than 30 seconds for real estate by using Photoshop. Here's how it's done…
Open your photo and the photo of the sky in Photoshop
Copy the sky you want to put on the home photo as a layer above the home photo in the same Photoshop document.
Duplicate the home photo and place it above the new background. So now you have the background sandwiched between photos of the home.
Change the blending mode of the top home photo to “darken”
Select the new sky layer and go to filter > camera raw filter. Change the exposure of the new sky to match that of the sky you're replacing. You can also add vibrance and color to make the sky more impressive.
Now all you have to do is a little cleanup. Put a mask on the new sky layer and mask out (paint with black paint) anywhere that the sky is showing up on the house. It likely won't cover much of the house.
That's it! It takes a little practice the first few times you use this technique to make it work on different areas, but you'll see over time that it's really quite simple to do. The trick is just figuring out the exposures of the sky and house so that the blending mode will work.