Once upon a time there was an affiliate link that paid me $5 per referred sale. I sent them Adwords traffic at 30c/click and a 10% conversion rate ($3/sale = $2

Once upon a time there was an affiliate link that paid me $5 per referred sale. I sent them Adwords traffic at 30c/click and a 10% conversion rate ($3/sale = $2 profit for me) until they eventually realised they could just do Adwords themselves. It doesn't matter if you're only converting 1% of advertising traffic if that 1% is profitable.