When you place an affiliate link on Facebook, you need to be clear that you’ll get paid if someone clicks on your link and purchases the product. There’s no specific terminology you need to use, but it does have to be clear that your link is an affiliate link. Even saying something as simple as “This is an affiliate link” before you place the link can suffice.
As an affiliate for Boatbookings, you will receive 20% of their revenue - effectively meaning your commission will be about 4% of any sales from your referrals. You also receive 10% of any commissions Boatbookings make on repeat customers who were your referrals. They do have a minimum charter value of 3,000 ($/€/£/etc) before commissions are earned.