I’ve discovered that it is VERY important to understand this about affiliate marketing — you are NOT a merchant, and customers from your site often do not understand that you are not a merchant.
On all of my affiliate marketing sites, I include a “Privacy” statement and disclaimer. On that page, I make it a point to say that “we are NOT merchants, but we partner with online merchants” somewhere in the statement. I have started making this comment bold faced type.
I doubt that it does much good to say this, because I continue to get email feedback from customers who click through my site links, make a purchase from the merchant, then contact ME regarding missing toy parts, broken or defective product items, etc.
You must do all you can to educate the people who come to your site that they are buying from your online “merchant partner,” not you, or you will always have trouble with this.