I personally unspooled a roll of 1000' RG-6 quad shield and ran it through a huge office Started on the roof, went halfway across the building, down a floor and into an IT closet. Installed a SWM dish. No problems. No amplifer. No service Call. That was 2 years ago.
Because of the difficult run, I even ended up cutting it about 400' into the line, and placing a barrel coupler on it.
When I was done, I had about 3' left on the spool. I was actually worried about it before I got there, I took one end of the spool tapped onto the dish, took the other end of the spool,(hanging out of the wood spool) and connected it. Worked no problem.
I was still worried the entire time I was running.
After reading your thread thoroughly, I was at a job today that had a longer run than 300'...Got HD....(This is a log Cabin in the woods)The DirecTV installer ran the line through the woods to a clearing and mounted the dish on a non penetrating roof mount on the ground(not very bright)...I hooked up to it today.
I have a feeling there's something else going on..Now if the customer had a bunch of RG-59 in the house, you may have real issues.
I have a feeling you got an installer that doesn't know how to site a dish in, or there is a line of site issue. (trees)