You might want to check out the FAQ section with contributions from myself and /u/g0dwinslawyer

In short, there are no real similarities between Sanders or any other self-described democratic socialist and the Nazis. One of the other problems of this line of thinking is that it is usually transpositioning twenty-first-century political definitions and American mores onto a mid-twentieth-century Central European context. What is "right" and "left" meant somewhat different things in 1933 Germany (and they still do in 2017 Germany!). This is an ahistorical and presentist way of thinking that contributes very little to understanding the complexities and contradictions of Nazi economic theory and its answer to the social question.

For one thing, there was a clear socialist party in Germany in the interwar period (the SPD and arguably the KPD) and a whole intellectual and political tradition associated with what socialism meant. Moreover, there were a number of answers to the social question throughout the German political spectrum. The SPD's approach tended to emphasize that it would serve as a midwife to the terminal stages of capitalism and enable a classless society. The NSDAP tended to draw from German conservative responses to the advent of capitalism. These ideas often prioritized racial or cultural solidarity would trump petty socioeconomic concerns if the right state structure appeared. The Christian Socials of nineteenth-century Vienna were one aspect of of this right-wing solution to class conflict and inequities. The German university system, which was a stronghold for German conservatism, produced a number of intellectuals arguing for close cooperation between the state and the economy. Many of the NSDAP's left-wing such as Hess or Goebbels developed their approach to economics in the German university, not from the SPD or other left-wing German parties. There was a longstanding intellectual tradition in the German university and in some German professions to see unrestrained capitalism as a foreign import that was fundamentally unGerman. In a similar vein, Hitler and his lieutenants' attacks on consumerism, department stores, and rampant profits had much more to do with cultural conservatives' critiques of so-called American styles of business penetrating Germany in the 1920s. There were very few partisans of free markets and open trade among the interwar German right; most tended to be clustered around the smaller bourgeois parties of the center-right. Most German industrialists and the DNVP favored protectionism and cartels, even if the DNVP also claimed to be the party of the small businessman.

If your friend still persists in this fiction, tell them there are many fine books on Germany and its politics as it relates to the social question. Avraham Barkai's Nazi Economics: Ideology, Theory, and Policy is one of the major books on the origins and development of the NSDAP's approach to the economy. Barkai asserts that the hazy economic program grew out of "Nationalist Etatism" from the antiliberal right of the Kaiserreich. Jonathan Wiesen's Creating the Nazi Marketplace is one of the better recent introductions to the issue of consumption in the Third Reich. Jeffrey Herf's Reactionary Modernism details the complex evolution of a particular set of ideas that embraced technocratic solutions and reactionary politics. Although it is something of an older text with turgid prose, Fritz Stern's The Politics Of Cultural Despair: A Study In The Rise Of The Germanic Ideology does convey something of the intellectual milieu of right-wing German thought over the nineteenth century.

For Bismarck's welfare programs, the relevant portions of both Lothar Gall's and Otto Pflanze's biographies of the Iron Chancellor are useful introductions. The Origins of the Authoritarian Welfare State in Prussia: Conservatives, Bureaucracy, and the Social Question, 1815–70 by Hermann Beck examines the wider climate of fear and reformism that pushed archconservatives like Bismarck to embrace a social safety net. Michael Stolleis's Origins of the German Welfare State: Social Policy in Germany to 1945 is a long-form survey of the evolution of the social question in Germany, including how the Nazis both continued and departed from older policies.
One of the things that is very typical among Reddit discussions of Nazism being left-wing is to uncritically examine the NSDAP's party platform and zero in on its commitment to social legislation. The problem with this is that the German welfare state predated Hitler by decades. Much of Germany's social safety net such as national health insurance, pensions, and other social insurance schemes originated with Otto von Bismarck. The Prussian Chancellor implemented these reforms- among the first of their kind- partly as a means to take the wind out of the sails of the socialists, but also because of longstanding Junkers' traditions of noblesse oblige. The Bismarckian welfare state proved to be quite long-lasting and all the major parties had to contend with them. Hitler's pushing of these programs was not an invention of his, but an adaptation to existing institutions. Some of Hitler's rhetoric was tactical in nature (ie "vote for us and you will get true help"), but there was also an element of trying to restructure socioeconomic relations along racial lines.

That was one of the key facets that distinguished the NSDAP from its contemporary rivals on the German left. German socialist tradition had an internationalist bent and officially eschewed racism. Discourse within the Third Reich almost always used national/nationalist in conjunction with socialist (eg National Socialist Welfare, National Socialist Automobile Club, etc.). This was not some arbitrary naming scheme as National Socialist ideologues constantly asserted that the Reich's solution to the social question was an unprecedented event in German history.

Response to a deleted comment

While the Nazis did rise to power by co-opting the left wing of German politics (which was later purged), by the time the Third Reich was in full effect little of the party's socialist platform was intact. Prior to Hitler, the Nazi party was more towards democratic socialist, but veered towards a weird corporatist "third way" position rather sharply.

This is fundamentally wrong.

The "left" as it was in Weimar Germany was represented by the SPD and far left by the KPD. These were major political parties and there was relatively little that the NSDAP borrowed from them, ideological or otherwise. While there was a popular stereotype of the "beefsteak" SA (brown on the outside and red on the inside), there was little in the way of cross-pollination between the SA's left-wing and the KPD or Marxist-Leninism. Most of the NSDAP's left-wing grew out of the German university system such as Goebbels, or various right-wing milieus such as the anticapitalism of the Freikorps which saw capitalism as fundamentally Jewish and unGerman.

While the NSDAP did have a left-wing, it was not "left" in the proper sense of the word. Most of its proposals were scavenged from various right-wing discourses. And even here, the left within the NSDAP had very little power. The Strasserite wing was muzzled well before the Night of the Long Knives at the Bamberg Conference. This ushered in a half-decade process of minimization of the Party's left wing or forcing those like Goebbels or Hess to toe the more centrist-far right line of Hitler.

If anything, the NSDAP co-opted the right of German politics. Although they made some inroads among working-class voters (often those who were ununionized), the bulk of the NSDAP's electoral support came from those German voters who voted on the right and middle of German politics. The hypernationalism and anti-Republican sentiment of the NSDAP was far more energetic than that of the mainstream conservative parties like the DNVP.