Will a 2005 shell fit a 2010, both 6.5 beds? What type of shop or person would I hire to install. Camper companies here said no, since I am not buying from them.

I wish to buy a camper shell, that was put on the truck in 2005, from a man who has a 2005 Silverado 6.5 bed. I have a 2010 Silverado with a 6.5 bed. When I contacted the local Camper Top dealers, they told me the shell will not work as the body's were different after 2007. They said if I purchase from them then they would install for $85 and guarantee the work. Is it a ploy by or does it sit a bit differently. As long as it fits without looking odd and will sit properly and safely on the bed I am fine.
Also I don't know what type of person/specialist/shop would put the cap on and do the wiring for the 3rd brake light. (Plus it has a rack on top, a LED light bar and LED flood lights on all 4 corners.