I don't see anything obvious with what you've posted.
Each receiver needs to be connected directly to the dish; one coax line for non-PVR receivers and two lines for PVR receivers. Any of the four ports on the LNB can be used for any receiver. No splitters can be used, and no switches are required for the setup as you've described it.
You don't state where you got the dish, so just be sure that if you have the 75e, the LNB is also marked "for the 75e" on the ticket attached to the LNB.
The power for the LNB is supplied by the receiver and goes "up" the same coax that the signal comes "down".
A zero signal strength ususally indicates a bad (corroded) connection or cable, or otherwise indicates that the receiver is not communicating with the LNB.
If the LNB was bad, you would get a zero signal strength, but you are right; it's unusual that the installer got a signal while you cannot. If this is truly the case, then it indicates that there is something wrong between the point where the installer made his connection to the LNB and the receiver.
If possible, I would take a receiver and a TV to the dish and connect it in where the installer connected his meter and see if this changes anything.
All that being said, you do not state if the installer had any Shaw Direct installation experience. If not, you need to evaluate his experience level and determine if you are confident with what he did. If your confidence level is low, I would begin by going to dishpointer.com and determining if the pointing of the dish looks reasonable. Also check the plumbness of the mast and the elevation and skew settings. If any of these pointings/settings appears incorrect, I would question whether your installer was being truthfull about the readings he got. I have read of cases where American provider installers have had difficulty doing a Shaw install for whatever reason.
I would investigate all these things carefully before investing another LNB. I think the chances of the LNB being bad are very low, especially if your installer's evaluation of the signal was done very recently.