@May136:
Many hosts, myself included, do charge a pet fee. Ours is $25. Make sure you mention the fee and amount in both your listing text and under the house rules section along with a requirement that they notify you when booking. After a guest books you can send them the fee through the resolution center (Send or request money link located in the left column of the guest's messages). We also charge a $50 fee per pet that "shows up" without advance notice. We've only had that happen once since adding that particular fee.