I attended Dale Carnegie courses early in my career, I believe they called themselves Dale Carnegie University but they never issued degrees. I did get some good pointers on public speaking and stress management. But would never compare that to a four-year college education.
Not sure "diploma mill" applies here.
The act of comparing Trump University to Wharton suggests that Trump is not what you might call a straight-shooter - that he'll say anything if that helps him get ahead, regardless of whether or not it's true. At the risk of understatement, there is some relevance to his quest for the presidency.
I don’t think Dale Carnegie claimed that you’d get a quality education beyond the courses he offered. Trump was saying that his education carries a certain credential that can be compared to Wharton. That’s different.