Craigslist Sugar Daddies have piqued my curiosity

These are guys pretending they aren't looking for a prostitute, looking for a prostitute who wants to pretend she isn't a prostitute.

Just to be clear - you understand that these Craigslist posts are solicitations for prostitution, and you're wondering if they're real or just jokes? Just to be clear: These men, if they are legit, are not looking to "help you out". They're looking for a young, hot woman that will fuck them for money. But beyond that, I have no clue if they're legitimate offers.

Hi, I'm a normal guy, and I would never post an ad like the one you describe.

Sounds like they're looking for a "kept woman."

It's men who aren't looking for a full blown relationship and all the responsibility that entails, but at the same time want more than a quid pro quo "I will give you $xxx for a sexual encounter" type relationship. They're likely using online personals (like Craigslist) because they want to find a person for this kind of relationship who is outside their normal social circles. Some ads are likely men fantasizing and/or posting just to see what kind of responses they'll get. Some are "legit" in sense that the men actually want (or think they want) this kind of relationship where some of the emotional commitment many women/gay-men expect is replaced with gifts or compensation. Some are men claiming to be that kind of guy because they think it's a tactic to shallow attract women/gay-men and get some action after an semi-expensive night on the town (because the shallow woman would think there's more coming and would decide to put out). People are weird, and get weirder when love/sex/loneliness/relationships are involved. It's impossible to paint a broad picture of what each of those posters are looking for.

Seeing as these types of set-ups happen in real life, why not advertise for it? Isn't the point of advertising to be upfront about what you want and have a higher chance of getting it, instead of randomly meeting people in everyday situations and trying to set up a certain arrangement (whether it be a sugar daddy situation or BDSM situation or whatever)?

I suspect that the style of ads you describe are really a response to the considerable stigma that (rightly or wrongly) attaches to men who are willing to pay for sex. The men refer to "helping out a poor student" or other justifications to make their solicitation seem less predatory and more mutually beneficial. This may increase their odds of getting a response. It might also assuage their guilt over seeking out prostitution.

They're men who want their own private hooker.

What Jacqueline said. They don't want an actual prostitute, because they want the girl for themselves exclusively. They take the girl shopping, pay her rent, buy her gifts, etc., and she has sex with him.