To the OP - general advice on this topic here on Flyertalk is:

- it is extremely unadvisable to sell miles (or more properly, awards) over the internet. Very likely to result in the airline finding you and cancelling your miles.

- It is somewhat risky to sell them to someone who you don't know pretty well. Your risk comes if the person flying is asked questions about you (how do they know you, what city do you live in, etc.) Sending a birthday card, mentioning in it that the ticket is a gift, signing "Uncle c0r5a38" might mitigate this.

- Least risky is selling them to a relative or close friend, who you can trust to keep their mouth shut.

Hope this helps.