Legal: yes
In accordance with the freq flyer program t&c:- no way! The ffp will close your account if they find out.
www.points.com seem to be the only web site that works with the airline ffp's

There is a long FT thread on these web sites selling miles/awards:- cannot find it just now

Edit:
http://www.flyertalk.com/forum/infor...solidated.html

not the thread I was looking for, but on topic http://www.flyertalk.com/forum/ameri...ure-audit.html

http://millionmilesecrets.com/2014/0...es-and-points/