What do you mean by "a good indicator ... to fraud and such?" Are you implying that fraud should be accepted as just something inherent in society and shouldn't be something we try and prevent? Also, I would contend that the facebook marketplace has less fraud than the craigslist marketplace, thus giving craigslist something they could shoot for.
Also, I'd like to refine "better" to "safer". General feel and aesthetics are subjective where as safety is objective.
Craigslist leaves millions, if not billions, of dollars on the table every year, it would only take the inclusion of one or two more markets in their pay-to-post-real-estate stream in order to hire some really smart developers to come up with smart and subtle fraud prevention mechanisms. It's possible for them to raise some dough for this issue without harming the culture, so why shouldn't they?