Mike,
Finding a new market is a "long/medium term" objective. In our case, we look at more than just the real estate statistics - we'll review demographic data (employment, net migration, income, permits, etc) and try to take a 360 degree view. The book "timing the real estate market" (Campbell) looks at a more formula based approach to evaluating when a market is ripe to invest and discusses these factors in more depth. Some of this data is available on a neighborhood/zip basis other only at the county level.
If the underlying trends in a market are poor then that will impact the DOM, etc.
As far as ARV - you can only do this by carefully examining comps. Also, make sure you account for time in your value. If the rehab is going to take three months look at what the neighborhood pricing has trended over the last two quarters and adjust your projections accordingly. Nothing wrong in investing in a market that is still trending slightly downward as long as you are adjusting your ARV accordingly.
FYI, if you are investing in regions that you do not know personally you need to final a local authority to bounce your investments off of. They don't need to be involved in your decision - just act as a sounding board; so you can be made aware of the new "garbage dump" or "drug and rehab center" that is beiing considered by the local council for approval just half a mile away! Your local team will pay dividends and the cost to keep them happy is a lot less than a bad flip.
TTFN,
Greg