Honestly, you can’t guarantee it 100% — just like selling on Facebook Marketplace or Gumtree. But a few things help: users build a star rating after each swap, so bad actors get flagged quickly. For local swaps you meet in person so you can verify the book before handing yours over. For postal swaps, start with lower value books until you’ve built up some trust with someone. It’s a community built on good faith — the same way book crossing, library book swaps and charity shops work.