I had an acquaintance who flew Dash-8 ferry flights for de Havilland (now Bombardier) to Europe, Asia, Africa and South America. They used ferry tanks where needed, but typically not to Europe.
The most interesting aspect of these flights was paying for fuel and fees. Many places would not accept credit cards, so my buddy had to stash wads of US dollars in various locations in the aircraft to prevent theft. I don't recall whether the buyer's pilots were on board these flights, or maybe their contract was to deliver the aircraft to the customer's home base.
Typically, in the case of a large jet aircraft, the customer takes delivery at the factory and flies it home, often as their first revenue flight. I saw one such aircraft a couple of weeks ago in Everett - it was an Malaysian (I think)767 or 777 - I was told that it will fly to LAX
and carry a load of freight to Malaysia.