Is e-signing 8879 sufficient or is there a separate e-sign process for 1040

[TX Newbie]

I understand that by signing the 8879 and checking the right boxes, the taxpayer gives permission to the ERO to sign the 1040 on their behalf.

BUT:
How is it guaranteed that the 1040 that the client reviewed is exactly the same as the one the ERO e-files?  1. How does the client know?  2. How can the ERO prove it if a dispute arises?

For 2., I can see how the ERO may be able to protect themselves in various ways.

But for 1., Is it the case that trusting the ERO and giving them permission to sign on their behalf is just one option for the client?  By checking different boxes, the client can also insist that they sign their own return? 
How would a client realize and understand these differences just by reading Form 8879 with all its mysterious terminology?  I came to this help forum because I could not with 100% certainty.
I would think that a client who can figure out what Form 8879 means would be perfectly capable of using something like TurboTax and filing their own return.

[TaxGuyBill]

When a taxpayer signs the 8879, they are effectively signing the 1040 themselves.

The 8879 does show the refund or amount owed, which should match the 1040.  Yes, hypothetically changes could be made afterwards, but if the refund or amount owed changes then it would not match the 8879.