It is very easy. You would get as many local realtors to come do complimentary market analysis, and challenge them to sell your "low price" competitors. You would use whosever service if s/he can sell your low price competitor.
If some realtor could sell your competitor, of course, you can believe what the one says, otherwise, you need to continue the complimentary market analysis.
When you continue calling local realtors, you bring attention to many realtors about the community. Believe or not, many realtors may have buyers, but just "not familiar with your neighborhood". So, say, if you bring in dozen market analysis, you "introduce your community to dozen more sales force".
I have found that after I invite close to 50 realtors to do market analysis on my community, the neighbors start selling, and of course, your low price competitors will be sold and many others will be sold too, and the market price will be coming back.
For example, this Edison Hollow South condo community is now SOLD OUT!! http://raspberryct.blogspot.com/
Why? There are only total 220 units, and I have invited over 500 realtors from the county to the community (there are total about 5,000 realtors in the county).