I made a simple webpage that fetches Nostr posts with the hashtag #NostrClassifieds: https://nostr.bitejo.com Few people are using it but if it would become popular, it would be possible to sort by location, category, etc. No custom post type or custom relay because it's just a simple way to advertise your products/services and doesn't handle orders, payments or reviews.

LNBits NostrMarket https://github.com/lnbits/nostrmarket is more complex and has more features. Maybe a taxi app could be added there. But in many cases the technical parts are easy, and the true difficulty is finding users...