Facebook Classified Groups - What Verticals to Promote

Hi guys;

What general verticals can be promoted in Facebook Classified Groups? Here in my country they are pretty common, and for each city there's 5-10 groups where people sell used electronics, clothing, etc...

I'm with a few accounts on MassPlaer on those groups, but I can't come up with an idea to promote. I tried to promote general shopping sites (amazon) but I was baed from groups, as people there are looking for used things.

Thanks