Building a micro-SaaS to aggregate P2P Magic: The Gathering offers from WhatsApp groups in Brazil — looking for feedback on the approach

In Brazil, the dominant platform for buying and selling Magic cards is LigaMagic. It works, but it has one fundamental limitation: sellers have to manually list every card. Most casual traders don't bother.

So the real market moved to WhatsApp. Hundreds of trading groups, thousands of active traders, posting card photos and prices every day. It's liquid and active — but completely fragmented. If you're not in the right groups, you miss deals. A seller posting in a group of 300 people is invisible to the other 10,000 traders elsewhere.

The solution I'm building:

A bot that monitors these WhatsApp groups and aggregates offers into a searchable layer on top of the existing informal market. No behavior change required from sellers — they keep posting in their groups as usual. Buyers gain:

• Search across all monitored groups
• Price alerts when a specific card appears below market value

Monetization: freemium — free basic search, paid tier (~$8–15/month) for real-time alerts and price history.

What I'm trying to validate:

Is this a real problem worth solving, or am I just building something for myself? Has anyone here tackled a similar "aggregate the informal market" problem in a niche community? What killed it or made it work?