>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.
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.