I do not, but that doesn't take away the fact that millions use the platform. It might gain traction, amongst Facebook users.
Chatting with friends is not the same as buying stuff. It can really poison the atmosphere. The very act that you could send money makes you less engaged.
1. see something you like
2. message seller and arrange meetup/pickup
3. upon inspection, pay via messenger
4. transaction done
Unlike other communication that is more ephemeral, it is very likely that any monetary transaction will be permanently and irrevocably attached to the facebook identity.