Referendum, swayed by state-of-the-art propaganda and nationalist sentiment, accepted as fair by government

Thanks to UKTV for examining in detail the Nazis' propaganda machine. In the second programme in the series, the authors explain how the Saarland plebiscite was a key step on the way to Hitler's domination of mainland Europe.

The requirement for a plebiscite was part of the post-Great-War settlement (the Treaty of Versailles). After fifteen years the inhabitants, until then under the trusteeship of the League of Nations, were to indicate the sovereignty under which they desired to be placed.

An Encyclopadia Britannica article takes up the story;
In the years 1933-35 the plebiscite dominate the life of the Saarland. The Liberty front - German exiles, Saar socialists, Communists, unionists, Catholics, Jews and Francophiles - defended the Saar against annexation by imperialistic Germany, which was favoured by the German front and the National Socialists. 

The UKTV programme explained the propaganda war. Joseph Goebbels distributed  "people's receivers" in the Saarland. These enabled Goebbels' sophisticated propaganda carried by the monopoly Reichs-Rundfunk-Gesellschaft (Imperial Broadcasting Corporation) to be heard throughout the region and to become the media-dominating messages. The Britannica article goes on:

Hitlerite methods influenced the vote which was held  on January 13, 1935, and it does not seem impossible that the vote itself was manipulated. Nearly 98% of all qualified voters appeared at the polls, an unprecedented showing, although the weather was bad and about 135,000 voters cast their ballots in a location other than that in which they were living. During the 18 hours in which the ballots were stored, Natinal Socialists had access to them. This fact was concealed by the official reports, which also overlooked discrepancies in the returns. Ninety and three-tenths per cent declared for union with Germany [...] on March 1, 1935, the Saar territory was handed over to the Third Reich.