An appraiser is tasked with using "like" properties. If your general area has a high number of foreclosures, then the market considers foreclosures as like properties. Note that some lenders are pushing appraisers to be more conservative (exactly the opposite of what they wanted just 12-18 months ago), so there could be a general push for the lower end of your market. The only way to know if there was a mistake is to have access to an agent who could pull comparable data for you. If the comparable data shows that foreclosures are not prominent, then you may have a debate on your hands with the appraiser.
While the lender is the client of the appraiser, ask the lender that did the appraisal if you can talk to the appraiser to understand their findings. But don't get into an argument with the appraiser, that won't be beneficial. Just ask straightforward questions, and listen to the answers. Then if you can get comparable data that shows the appraiser should have considered different data, then you might present that in a second call to the appraiser and ask them why they didn't consider some of the comparable information that you've discovered.
Best of luck,