These are two entirely different questions.

I am not aware of restrictions on trading or selling Amex points. I've noted in this forum that I have bought points from co-workers. As mia noted, in theory you may deposit points only to the account of an authorized user on the account, but the Amex website seems to create no bar to doing this. While buying and selling points is prohibited on FT, trading points consistent with the rules of Coupon Connection is allowed.

However, the points brokers are a different matter. If you transfer your points to your FF account and then book an award in someone else's name and are compensated for it, you are clearly in violation of the FF program's rules. The FF program can clearly invalidate the ticket and confiscate your entire FF account. In practice you can probably get away with it once or twice.

If you transferred your points to someone else's FF account, as noted earlier, this is not something Amex is supposed to allow you to do, but they don't seem to prevent it. However, I really doubt the point brokers will want you transferring points to THEIR account. That would be a huge red flag for the airlines, noting frequent large transfers in and bookings out in multiple names.