Losing some money to protect your brand and product is necessary. You have to show them that you will defend your brand and will not bow down to their threats. Most of these are Chinese sellers using FBM. After a while, they will back off and go where the resistance is lower. I have been through that. And if your C&D doesn't work, and if you think your product is worth engaging a lawyer to watch over, do spend some to get a lawyer to send the C&D in their legal letter head. It worked for us.