Can you tell us how you're resizing the image and what editing program you are using.
As an aside, I'm just completing a fairly comprehensive article about Digital Photography for real estate agents including how to address some of the problems encountered when taking photos of buildings, homes, etc. If you're interesting check back in a week or so, it should be complete wilt all segments of the article linked:
http://www.digicamhelp.com/digital-cameras-and-photography-for-real-estate-agents/index.htm