Ive never used these guys for a network install, but they have done TV wall mounting for me and people I know in the past and were really good. They are also subcontracted out by Richersounds for their installs.
They aren't the cheapest I've seen, but cant fault their install on my TV mounting and general appearance and attitude of the two guys that came. Even helped me hang my TV on the bracket and move my unit back after they were done.