I agree that it's best to just go the DIY route. For a 55" LED I recommend that he get a friend or neighbor to help him mount it.
Depending on how he wants it installed this may not be a DIY job. If you just want the TV on the wall and wires running down the wall (or hidden behind one of those pannel things that run down the wall) then yes it's DIY but if you want wires hidden and plug not showing then it is not a DIY job.
http://www.cinemainnovations.com/ Give Jason a call. That guy is really good. Will save you a lot of time trying to do this yourself
Nope, that still can be a DIY: LINK Though, I understand that some may not be comfortable with doing it.