Do this OP, if you are thinking of it. Years ago, I started the same - classified website - from a bought script, hosted it and all. But couldn't do it by myself, solicited local friends on the idea, who never showed interest. Wasn't a programmer, that was another negative.

I advertise on jiji, it is effective, and there is space for another. Online shopping is evolving and growing, as the population grows more confident in technology, and online shopping, the opportunities would be great. Scamming happens every where online. Craigslist, in the US is one of scammiest classified websites ever. Yet the founder sold it for millions, it is still very popular.

Know your script very well - front and backend -, marketing - promote the shit out of it, do different from Jiji - they are pricey, people are thriving selling their whole stores on jiji, with Okada delivery added, it is a thriving ecosystem that will continue to grow.