As a dealer and professional installer, as far as im concerned anyone who installs systems in the winter should guarantee the placement of the Dish due to trees in the spring for the first year.
Now in the 2nd Spring, if the trees grow its not my problem!
I have been doing this for almost 8 years, and when I was installing full time I would usually tree out about 2-3 jobs per year. Situations come up where its a tight look angle, and I needed the money so I went ahead and installed.
When the trees bloomed in the spring, customers called me up and I went back to their homes and fixed my mistake at no charge to the customer.
A few of them we knew there would be a problem, and we let the customer be aware of this and told them to call us if it was because it was too close to call. Other times the trees will actually grow.
The only ones I do not fix due to tree issues are customers who went into non-pay disconnect during the winter that caused DISH Network to chargeback my installation monies. When those customers call me up, I laugh and tell them to take their problem up with DISH.
Anyways, the biggest issues with all of this is the fact that when I do an install my money is subject to chargeback for 360 days. I don't fix it, the customer doesn't get their problem resolved and they disconnect and I get charged back. When these companies or contract installers install your system, they are subject to 90 days, so after 90 days why should they care if its pointed into trees.
As far as the customer signing off on the work order taking responcibility for the install, the responcibility is still on the technician. The customer doesn't know any better where the Dish should or should not work.