Firstly, you do not need to remove your data from our Mac before sending it to us. We are a registered data controller with the ICO and qualified to handle data-sensitive IT assets. We have a data processing facility where your item will be processed, its data professionally removed using our enterprise-level tools, and a data destruction certificate generated.
If you would prefer to wipe your Mac before sending it to us as this would give you peace of mind you are more than welcome to.
However, what is important is that you sign out of your Apple ID.
Not doing so will prevent us from being able to wipe your system as it will be locked to your account. To sign out of your Apple ID see the official support guide here.