I agree with you that it may not be such a good deal afterall.
Clarify with Direct TV if you are Buying a receiver for the money or renting it.
I know that you have to pay $5 per receiver for mirroring charge for your programming..
BUT if that is the ONLY fee you have to pay, then buying used is a terrible Idea.
There will often be a charge for the accesscard if it is missing or invalidd and this could be $40..
Seems like a lot of trouble to go through to get used equipment without a warranty that is the old model and probably slower with fewer features all to save $30..
Also... You said you have a triple LNB dish..
How many outputs does it have going into the house?
Does it have two wires or 4 wires that can lead to the house?
If you don't have the right switch, then it will still be hard to hook up.