Yes, those so-called tax foreclosures are too good to be true. However, for tax foreclosures, call your local city or county government. Most jurisdictions put tax foreclosures up for sale once or twice a year. Your locality can tell you what the schedule is. The notices will also be published, generally in a newspaper serving the area. And probably posted on the jurisdiction's web site.
Without going into all the details, generally the tax foreclosure is only one small slice of the entire "pie" of debt on the propetry. And often the property has been allowed to go to tax foreclosure because it isn't worth anything--a landlocked sliver of land, or a chunk of land on an unbuildable flood plain.