>the fact that they cover the country, and that everyone, even very non-technical friends of mine, know what it is That's why after you build the free version,

>the fact that they cover the country, and that everyone, even very non-technical friends of mine, know what it is That's why after you build the free version, you name it something similar, eg: freelist or joeslist. Now people get the gist of what it is just from the name, you can't be sued for copyright and you're a valid competitor. Craigslist is undoubtedly a useful service but it's trivial to implement and the only reason to use craigslist over some competitor is because everyone else uses craigslist. If you place a barrier to entry, you lose customers unwilling to pay. If you lose customers, you lose other customers.