Just looking at closed single family homes from January 1 - April 30 of each year:
2010: Average sales price was $331,620
2011: Average sales price was $313,126 - a decline of approximately 5.5%
2012: Average sales price was $296,110 - a further decline of approximately 5.5%
So, with just this small bse of data (4 months' worth each year) we see about an 11% decline over the past two years in Bethel. This is based on the data entered into the Greater Fairfield County Multiple Listing Service, which is assumed to be accurate.
Of course, these numbers may vary based on individual market segents within the town of Bethel.