Please don't tie Facebook to logins on other sites. It excludes half the population of the US, more in other countries, and if you add a non Facebook option, the scammers will just use that.
Craiglist's solution is simple--their exhortations to only deal locally means that if I'm looking for a house or a car, I will see it before I give money. The scammers are aiming at people that ignore that rule.
Plenty of people buy and sell long distance on Craigslist, but that is really a caveat emptor situation outside of how the site is intended to be used.
I've seen a bunch of my friends use Facebook as a "pre-craigslist" as in "if none of my friends want it first, I'm going to CL this TV"
I would feel much more comfortable buying something through a friend or a friend-of-a-friend. And I would start to consider more risky things (e.g. finding a babysitter) through Facebook that I wouldn't ever do on CraigsList.
