Airlines are cracking down on people engaging in sale or barter of miles. This is against the T&Cs of FB and other airlines.

There are been other posts on FB and other airlines regarding the exact (and formerly common) procedure that you describe:
- Open a FB account just for the purpose of issuing awards
- immediately transfer the exact number of miles for awrds from AMEX
- issue awards to unrelated pax.

This was a most common and obvious procedure that can be easily detected and leads FB to freeze your miles. Then FB makes you go through various hoops to establish that it is not a transaction linked to selling miles. The burden of the proof is not on FB as they can decide to withdraw the miles in your account at their discretion at any time.

Apparently, you just opened a profile on FT for the purpose of investigating what you can do. If you read other threads, you will see that it is not an uncommon problem (BA has been auditing many accounts too). My suggestion is that you simply accept that you were trying to sell miles and got caught. That is unless you can prove that the awards were issued in the names of family or close friends.
It might seem strange to you that the burden of the proof lies with you, but the T&Cs that you agreed to give FB a lot of leeway.

Article of T&Cs:
1.4.7 The sale, purchase, brokerage, resale, barter or exchange of Level and Award Miles, Award tickets or vouchers for any compensation is prohibited, except as otherwise provided by the Company in accordance with specific terms and conditions defined in FB Communication. Violators, including any passenger who uses a purchased or bartered Award, shall be liable for damages and litigation costs. Level Miles, Award Miles and Awards have no cash value and can never be redeemed for cash.