Why does Cypher believe that Smith would keep his part of the bargain?
Who said he did?
First we have to understand just how much Cypher hated the real world. From the script:
That's what he said to me nine
The meat is so perfect, charred on the outside, oozing
red juice from the inside, that it could be a dream.
The real world. Ha, what a joke.
We recognize the grating voice, the insidious laugh.
You know what real is? I'll tell
you what real is.
A fork stabs the cube of meat and we FOLLOW it UP TO the
face of CYPHER
Real is just another four-letter
He laughs, shoving the steak into his mouth.
The restaurant is located on the top floor of a Chicago
skyscraper where the view is breathtaking and the menu
has no prices.
Sitting across from CYPHER
is AGENT SMITH
Do we have a deal, Mr. Reagan?
chews the steak loudly, smacking it between his
Mmm, so, so fucking good.
Smith watches him shovel another hunk of meat into his
You know, I know that this steak
doesn't exist. I know when I put
it in my mouth, the Matrix is
telling my brain that it is juicy
and delicious. After nine years,
do you know what I've realized?
Pausing, he examines the meat skewered on his fork. He
pops it in, eyes rolling up, savoring the tender beef
melting in his mouth.
Ignorance is bliss.
Then we have a deal?
I don't want to remember nothing.
Nothing! You understand? And I
want to be rich. Someone
important. Like an actor. You
can do that, right?
Whatever you want, Mr. Reagan.
Cypher hates the real world. He's willing to sell everyone out just so he doesn't have to experience it. What risks would he be willing to take to get out of it and back into the Matrix?
This is obviously not canon, but I imagine it to be similar to Azrael in Dogma:
Human, have you ever been to Hell? I think not. Do you know that once Hell
was nothing more than the absence of Cod?
I'd rather not exist than go back to that. And if everyone has to go down
with me, so be it.
He's willing to let all of humanity suffer so he can not be in the real world anymore. Being betrayed by the agents is a calculated risk that he seems to be willing to tolerate.