In this:

http://www.itv.com/news/2018-04-23/martin-lewis-to-start-legal-case-against-facebook-over-scam-adverts/

Facebook say "when there is a fake ad, martin should tell us and we'll deal with it" but he doesn't even advertise on FB.

If someone posted an ad pretending to be me, I wouldn't know because I don't use FB.

so - who is responsible here FB? or is it more complicated?