If they're RealtyTrac listings, the prices are incorrect. Not sure why they're permitted to put that information out, but the information is not correct. Let's leave it at that.
In some areas of the country, those are real prices. Depressed areas, like Detroit, upstate New York, and some areas of the Midwest.
In some areas of the country, properties are just cheap. Spartanburg, South Carolina, comes to mind. You can find real properties there very cheaply.
In some areas, the properties are in terrible condition, as is noted by other answers already. There are shells in Baltimore you can buy for $20,000.
In some cases, those are the real prices for manufactured or mobile homes. I sold a very nice 2 bedroom/1 bath manufactured home in a very nice community in the suburbs of Washington, D.C., for $14,000 last summer. Comparable condos were selling for $90,000. You can buy nice 3 bed/2 bath manufactured homes there for $40,000-$60,000. The first question I'd usually get was: "What's the catch with the price?" No catch. That really was the price.
To determine which of those categories the houses you're looking at fall into, find a Realtor and have the Realtor do the research.
Hope that helps.