Police merely state that they received reliable word from a reliable source. No judge will make them elaborate or name names. After all, the informants identity must remain silent to protect their sources. This is how a substantial number of narcotics raids are initiated.
In most states, someone can appear in front of a magistrate and swear out a warrant with no questions asked. If their story sounds plausable, a warrant will be issued and ultimately served. The person named in the warrant gets dragged to jail in handcufffs, get their car towed to impound, then appears before a magistrate and begs not to remain in jail for a month or two until the date of court. Happens every day. Very little recourse unless you have big bucks to keep a lawyer interested for a month or two.