If Craigslist charged $1, users would immediately flee to any new competing sites
People who post ads would, many of them. The question is whether people who read and answer ads also would, or whether the improved quality of ads would cause them to stay, making the competing sites unattractive due to the lack of an audience and finally forcing the posters to return to craigslist. This is what happened with ebay.
The question is not whether posting an ad is worth $1 to you, the question is whether having your ad read by enough people is - and for that to be true, enough people must find looking the ads on the site worth their time.
People who post ads would, many of them. The question is whether people who read and answer ads also would, or whether the improved quality of ads would cause them to stay, making the competing sites unattractive due to the lack of an audience and finally forcing the posters to return to craigslist. This is what happened with ebay.
The question is not whether posting an ad is worth $1 to you, the question is whether having your ad read by enough people is - and for that to be true, enough people must find looking the ads on the site worth their time.