It's been my experience: Craigslist is the biggest waste of time on the planet. People don't provide many details about their bikes. They don't describe frame size, quality, etc. After you spend hours contacting people or driving around looking at misrepresented bikes, you pay dearly for the occasional bargain.

The problem with Craigslist is twofold:

1) No structured data entry. They don't solicit commonly-expected data elements like year, brand, model, frame-size, color, wheel diameter. It's just free form, giving advertisers little guidance.

2) No reputation system. If a seller misrepresents their bike, how will it affect them? There is no buyer feedback or history. (Think eBay.).

For the new rider, they wouldn't know what to even look for. It would be like rolling the dice on Craigslist. The experienced rider might know which bike(s) they're looking for. But, they're going to work for it. (Watching CL for weeks, soliciting information the seller didn't provide, driving around only to find misrepresented bikes, etc.).

I think the reasonable choices for a new rider are discount-store or bike-shop. The bike shop will give them an education on riding styles (road, cafe, fitness, comfort, cruiser, hybrid, mountain). Also, an exposure to brands and frame sizes. But, the rider will pay for that.

People opposed to discount-store bikes make a good point that the new rider may not be willing to invest the time to make such a bike work. They may get the wrong bike and have aches/pains/injuries that will turn them off of riding. Those are definitely risks. But, there's also the problem of a new rider not willing to plonk down $400 on a bike-shop bike, not knowing if they'll enjoy riding. They might not ever give it a try.