If you are interested in all the latest programming (local channels, HD etc) the installer could be right or it could be very difficult to do. I had installer tell me same.
However, since I am in a rural area with no cable or over the air reception, some TV was better than no TV. I was perfectly happy to just try to get the 101 sat for basic programming and didn't care about local or HD. So I did a DIY install and got reception.
I am surrounded by trees plus a high hill in direction of satellites. So before buying system and doing install, I obtained the azimuth and elevation setting for my location for round dish (off Direct TV web site). Got a good sighting compass and started looking for openings in trees or location I could possibly aim over trees in direction of azimuth bearing. Nothing from ground so got on roof and checked again and was able to locate a suitable mounting site.
When looking for a "line of sight", you have to also consider the elevation angle. Mine was 40 degrees which means the satellite is pretty high in the sky. I understand the dish actually "points" below the satellite for the proper reflection angle so the satellite is actually somewhat higher. So take into account the elevation as well as the azimuth when looking for "line of sight".
I don't think you need a very wide opening either as mine is only about 15 feet side to side but is clear above. Trees may eventually grow to block signal but will worry about that when it happens.
So with some effort in it, was able to find a roof mount location to aim between some trees and over others to get good signal. So much for the installer's "you'll never get reception here".