paying way too much for crappy coverage
They all say that.
You need more specifics.
What do they like about the plan? What do they dislike? They say they are paying too much. This is based on what? If they haven't looked at other plans they don't know if they are paying too much or not.
guaranteed deal even if we were to quote the exact same coverage at $1 less a month.
One of two things jumps out.
If they will move now for $1 less, then what will they do when someone comes behind you saving another buck?
There is something going on here beyond price. Do they hate the agent? If so, ask for an AOR (if BX will allow it).
If they don't like service, then how do you prove carrier X will give better service?
You really need details on why they don't like their current plan.