[welldressedgent]

This seems like a terrible idea. Sooner or later, you'll fail to complete a run. That will count as a broken promise, and you'll be stuck with a permanent curse.

[Jack_Spade]

Only if you make dumb claims: just tell the Johnson honestly, that you'll do your best to finish the job.
Don't make promises you can't keep

[welldressedgent]

I always had the impression these meetings promised "we'll do this." Not, "We'll try our best." Some adventures explicitly murder shadowrunning teams who fail, so that doesn't sound like they want to hear "I'll try."

[Overbyte]

I don't think doing your job falls under the umbrella of a "promise" not in this sense.

You don't "promise" to do a job. You take a job and try to do it to the best of your ability. Failure means you get a bad rep unless there are extenuating circumstances. Sometimes Mr. Johnson might even hire you for a job that he knows will fail.

[Marcus]

It's very Simple. "I promise to do my best to complete the Job". But even that is unnecessary your Johnson, isn't gonna take sworn oaths on the subject, and if he does then it's time to walk away.