the matrix - Why did Cypher trust the Agents?

In the first Matrix film, Cypher makes a deal with Agent Smith (to forget about the Matrix and to be put back in as someone rich/famous) betraying Neo, Morpheus and everyone else, in the hope he would be given this new life …

I would have thought that the most likely outcome for Cypher, and the easiest for Agent Smith, would simply be to have had him killed once he was no longer useful. Surely a traitor like Cypher would be wary about his deal.

Why does Cypher believe that Smith would keep his part of the bargain?

Answer

Cypher's act is one of desperation and bitterness. He is bitter because he knows Trinity is falling for Neo. Had she not done that, Cypher may have continued to be loyal to the Real World group. Without her he just regrets the hardships and misery of living without all the comforts of being inside the Matrix. It turns out he probably didn't have a reason to doubt the trustworthiness of the Machines.

In the first Matrix we see Agent Smith trying to deal with Neo in order to find Morpheus.

My colleagues believe that I am wasting my time with you but I believe that you wish to do the right thing. We're willing to wipe the slate clean, give you a fresh start and all that we're asking in return is your cooperation in bringing a known terrorist to justice.

Later when negotiating with Cypher

Agent Smith: Then we have a deal?
Cypher: I don't want to remember nothing. Nothing. You understand? And I want to be rich. You know, someone important, like an actor.
Agent Smith: Whatever you want, Mr. Reagan.
Cypher: Okay. I get my body back into a power plant, you insert me into the Matrix, I'll get you what you want.
Agent Smith: Access codes to the Zion mainframe.

Cypher: No, I told you, I don't know them. I can get you the man who does.
Agent Smith: Morpheus.

It isn't clear to me how they knew that some of the people from the Nebuchadnezzar got back to their ship (out of the Matrix), but somehow they did. It is only then they decide to deploy the sentinels in order to kill everyone and keep Morpheus in the Matrix.

Agent Smith: Never send a human to do a machine's job.
Agent Brown: If indeed the insider has failed, they'll sever the connection as soon as possible, unless...
Agent Jones: They're dead, in either case.
Agent Smith: We have no choice but to continue as planned. Deploy the sentinels immediately.

It is in the third Matrix we get the feeling that the machines (or programs) can be counted on to be trustworthy once a deal has been struck.

Oracle: The ones that want out.
Architect: Obviously, they will be freed.
Oracle: I have your word?
Architect: What do you think I am? Human?

Maybe having studied Machines for most of his life Cypher knew that they could be trusted to keep a deal once one had been struck.