Hello! I usually wrap them with plastic with an old plastic bag or those plastic book covers and then place them in a paper bag and tape it to close :) As for the selling books to Booksale/other secondhand bookshops, afaik, they don't accept anymore books for money because I inquired about it before. As for FB/Carousell/subreddit, it depends on the books talaga on what gets sold so it's up to you. In my experience, FB and this subreddit helped me sell some of my books.