I would suggest that you get a vendor, who is known to back up their warranties with actually checking on the installation quality and willing to work the issues out. No other vendors I know EVER visit installation site or do they really care about how the installation went beside of looking at test results.
One other point is: if someone is able to provide you with Systimax warranty, you can be sure that you can trust this installation company because the selection process is the toughest in the industry.
Higher price also has a lot to do with high quality and performance of components (though they are not always easy to work with).
I guess, nobody can argue with the point that higher prices also reflect marketing achievements of Avaya folks. But isn't it the way all markets are?
Dmitri Abaimov, RCDD
P.S. At this point in time I am not employed by the manufacturer.