How do I tell if a record exists?

Searching for a user using cURL like so:

curl -iL https://orcid.org/0000-0000-0000-0000

Will return a 200 even if the user does not exist. To avoid this, use content negotiation in your call like so:

curl -iL -H 'Accept: application/xml' https://orcid.org/0000-0000-0000-0000