I worked in a small company, which were easier to ask to extend overseas trips, since the ticket fare was the same or less than returning at the end of the business part.
Only one time the heir of one of the the company complained about it (it was a 3-day training overseas, Mon-Wed, I had the green light from my boss, sales director, the Thu & Fri came from due vacation period, I was going other city nearby and will pay all my expenses).
He called me Wednesday morning to complain, I told him OK, I could return today, please just send a new ticket and refund me of my personal hotel reservations and expenses already paid.
There was no reason to need me back at the office 2 days earlier, he was just p** off because I was "taking advantage" - a thing his father (and himself) used to do all the time. Ok, they were the owners...
Later I found he was really willing to pay everything, to teach me a lesson, but when he asked mommy (finance director) to change the ticket, she told him that she had agreed with, even because the air fare was cheaper with me staying more than one week instead of only 4 days, and I had overdue vacations.
But OK, if he really wanted it, she would reimburse me and the extra company expenses with the new ticket (same day int'l fare...) from his salary.
For some reason he stepped back...
PS: he was at his late 20's, he was the managing director, and it was (and I'm pretty sure still is) his first and only job since he finished college. I was with he company from almost 10 years, and I had did it before with no problems, but this was the first time I asked for it since the he joined the business.