Should a reviewer trust promises made in the rebuttal? Many Computer Science conferences offer a rebuttal phase, and it often does not require the authors to upload an updated version. Instead, the authors clarify things and many also make promises. What are reviewers supposed to do with these promises? Should the reviewer trust it or ignore it? The promises may not be fulfilled at all eventually.
I thought about this a lot when I first started reviewing for conferences and discussed this with other people. I will give a sum up how I handle it as a result of these discussions but it seems to be a quite controversial question. 

I choose to give the benefit of the doubt except there are explicit reasons not to. Rebuttal periods are normally one week and limited to 1 or 2 pages, there is only so much additional results that can be produced and included. Also, generally doubting the sincerity of all authors is not feasible on the long term. You might also doubt that the numbers they report are not true because you do not have the code to check it. 

Although it was not really the question, the second part is about how to avoid only getting promises:


Precisly state in the review which of your concerns are crucial for acceptance. I often see reviewers who do not make it clear what their priority for the rebuttal is and then the rebuttal is full of replies to minor comments. (For example, stating all the parameters used for training is useful in the paper but not useful in the rebuttal.) 
Phrase your actual concerns instead of saying which additional experiments/comparisons would ease them. (The difference between "Please compare to initializing with this baseline" (easily promised) and "I do not see why this complicated strategy should be better than this simple baseline") In my experience, this leads to more interesting answers.