Forgetting the right and wrong for the moment, is this the situation now?:
¶ according to the US Embargo Act and OFAC (Office of Foreign Assets Control) guidelines nothing (barring a few intellectual exceptions) can be imported from Cuba whether they originated before or after 1962 (about the time of the Castro Revolution).
¶ but the US Embargo Act and OFAC guidelines allow buying and selling within the U.S. of Cuba items originating from before 1962 -- as long as they were not exported from Cuba after 1962.
¶ but eBay (to make enforcement easier for itself) has a stricter ban -- it won't allow any selling of Cuban stuff regardless of the date it originated in Cuba because there is no way for sure to tell when the stuff left Cuba (that is, before or after 1962).

So to give an example:
¶the U.S. doesn't mind if a coin left Cuba before 1962, and is being bought and sold today in the U.S.
¶ buy eBay won't allow it.

Robert