will

I would go with would here. It sounds as though the person has already failed to deliver on their promise.

Blue JayI would go with would here. It sounds as though the person has already failed to deliver on their promise.

What if the deal is still on just that he wanted to go back on his word? Is would still the best answer here?

I'm not sure if I should use would or will because it is a sentence said in the past.

Thanks!

Yes, he said at the time "I will do X". At the time we could have reported it to someone else as "He says he will do X" or "He said he would do X". Now the original conversation is well in the past, so we would now report to someone else "He said then that he would do X, but now he says that he will not".