To retrieve the data for a particular eBay user, use GetUser. If an application already has permission to execute a GetUser call on behalf of a specific user, no request fields are needed to make this call. An application can also retrieve user information for another user without getting explicit consent from that user, but some data will not be returned, including that user's email address as well as their eBay subscriptions. To retrieve user information for any eBay user without their explicit permission, the UserID field in the request payload must be used, with the eBay user's user ID being passed into this field.
The default GetUser response does not include some fields related to selling and selling feature eligibility. To retrieve this data, the IncludeFeatureEligibility boolean field must be included in the request payload and set to 'true'. If this field is set to true, the QualifiesForSelling boolean field will be returned to indicate if the eBay user is registered to sell on eB
Uniquely identify a user
While the value returned in the User.UserId field of the GetUser response uniquely identifies an eBay user, this value cannot be relied on 100% of the time since an eBay user may choose to change their eBay user name associated with their account. A more reliable eBay user identifier is the User.EIASToken value returned in GetUser response. The EIAS value for a given user does not change, even if the eBay user changes their eBay user ID. Since the User.EIASToken value cannot be modified for an eBay user, an application might want to store this value along with the eBay user ID.
Note: The unique user identifier returned in the EIASToken field has nothing to do the authentication token that you pass in through API calls. The EIASToken value cannot be used in any Trading API calls to identify an eBay user.