Sounds like you found out after the deal what they might be worth (might be since we know internet prices aren't always the going local rate) and that the seller was looking for a good home for them instead of letting family ignore or neglect them.
If he didn't need the money and you didn't know how good a deal you were making until after the deal was done I don't see any ethical quandary.
If he didn't need the money and you didn't know how good a deal you were making until after the deal was done I don't see any ethical quandary.