I started selling on different groups on Facebook 6 months ago. I had success selling stamps on a couple of groups. I tried diecast groups but it's not as easy. You can sell on lots of groups including local community groups - but it does depend very much on each individual group - some won't allow you to sell, others let you sell but want specific sales methods for safety, others want only Obey sales.
Remember whatever you collect there will be a group on Facebook - toys, games, stamps, furniture, radios, - they've all got groups and with research you'll find them and some groups will allow you to sell there.
Hence I told Bitty about the furniture restoration group - its one of many!
As for ebid promotion, I've been using a compliment slip for 20 years saying 'thanks for buying' and giving details of what to do if the buyer has an issue. Works fine, as I then put a sticker on to say - I sell on eBid - however most ignore it. It's only recently that I've started doing it on Vinted, so we'll see how it goes and I'll report back.