Ted,
You've just been given a great education on Comp selection. However, I notice that you're from Minnesota, which may or may not present new problems.....lack of comparables. I relocated from an urban area of Northwest Ohio, where most often comps were plentiful, to Northern Michigan, where I'm sometimes lucky to find 1 "good" comp and fill in with anything else available. So here's my add-on to the previous posts:
I start with location - it's the realtors' battle cry and extremely difficult to adjust.
My second step is to determine, in order, what subject features bring the most value to the subject. This is where knowledge of your market is imperative. This varies from market to market. Up here, water frontage is the dominant feature in determining value. If the subject sits on 10 acres, I try to find sales of 5-15 acre parcels. I try to match size within a couple hundred square feet. We rarely have the luxury of similar style homes but I do try to get close on age/condition. Quality is another difficult market adjustment to make because rarely will the same buyers be interested in different levels of quality.
Then there are secondary market expectations. If your subject is a manufactured home, then they will want at least 2 manufactured sales. Likewise, you will need to support the value of the features such as 2 bedrooms and basements or crawls and wall or space furnaces. That being said, while it may not be a good comparable by traditional guidelines, if there is only one 2-bedroom sale and your subject is 2-bedrooms, you'd better include it instead of one which may actually be a better comparable. (Up here, 2 bedrooms does not impose the functional obsolescence it normally does due to the large volume of 2 bedroom homes which, oftentimes, started as cottages.) Six month sales is rarely achievable since our winters last 5 months and effectively diminish the real estate market.
One last piece of advice which I received from my Mentor and has been worth gold to me during my career: "There are always comps. They may not be good comps, but there's always comps." When you get tough assignments, you may have to loosen your search boundaries to find the most similar market sales. I've used comps which would be laughed off the form in urban areas where sales are plentiful, but they were the only relevent sales available. :usa: