Yes, I agree with you - Facebook groups are much more personal and interactive. It's hard to buy or sell to strangers who you have to communicate through e-mail, or text or call you. Also, scammers and spammers like you mentioned, is absolutely a nuisance in any classified ads website. I know it comforts sellers and buyers when they see who they're dealing with. Communication is key and I believe that Facebook groups deliver that better than Kijiji.
That's great insight on ways to find or post efficient classified ads, a lot of people don't know about the powers of Facebook groups!