Yes (no experience selling, but buying).

After they follow the instructions (assuming creating a new account) the first time they connect it for Bodymedia Sync to transfer the profile data it will say something along the lines of "data already exists on the device, do you want to delete it?" They click yes, the device starts using their profile data to calculate calories burned.

Other situations, like the person already has a Bodymedia account or old device, or you are also giving them your Bodymedia account (AFAIK the only way to transfer a subscription) are also possible but would involve a bit more work on their part (e.g. might need to keep some of the Bodymedia profile data, might need to delink and relink some linked accounts if switching device, and I believe earndit has an issue if you change Bodymedia device that might require technical support from them - don't think they have a delink option).