When hiring a real estate photography service you get a higher quality final work for several reasons.

We use professional machine bodies, with larger sensors that avoid noise in the image, capable of capturing a greater number of colors. 
We use lenses that allow for more detail, achieve a realistic appearance and avoid distortions.
We obtain stable images using a tripod.
We use techniques such as Flash and HDR to control the difference in light between exterior and interior.
We edit the images with professional photography software.

These are some of the reasons that make the difference, but the main one is the acquired knowledge of specific techniques adapted to Interior Photography.