Link exchanges simple involve a business finding related sites and asking them to house a link from their website to the business’s website in exchange for giving the related site a link from the business’s website. These are generally free and can help to increase a business’s ranking with some search engines. Alternatively, the selling business will be charged a fee on every sale arising from the link exchange (‘pay per sale’ as opposed to ‘pay per click’). This is known as ‘affiliate marketing’, of which Amazon is an example.