Okay everyone just get a handle. No one sold miles, no one bought miles. The miles are non transferable as per BA's legally binding T&C, and most if not all other mileage currencies. You don't even own your own miles as per the same. You may have certain rights as the accountholder but that's about it. If, in a mileage sale one side decides to screw over the other, the injured party would have no remedy by courts.
So everyone stop hocking with קנין, מקח טעות, אונאה, זוטו של ים, אוא"ו. Clearly you want to keep your word and as you got $ you won't just run off with the miles, but this should definitely be subject to the norms of the industry.
One more thing - if your wife had the account before marriage it would be נכסי מלוג and you'd own a קנין פירות