Reviewing demo papers, poster papers or extended abstracts I have a fairly straightforward approach to reviewing papers: I start by figuring out the main claims the paper makes, and figure out how those claims are proved. From there I start "zooming in to the details". But the primary question is always: does the paper make a claim, and if so, is it proved?

However, some tracks of conferences do not require a full paper. Instead, they require short form papers or extended abstracts describing what the authors will do at the conference. For instance, describing a poster or a demo they will present. 

What are some general criteria/strategies for reviewing such papers? How can I come to a well-reasoned decision to reject, if there are no "mortal sins" (like a flawed evaluation) for such papers?
IMO, the following guidelines might help:


Extent of novelty 
Quality of the figures and tables
Dedication 


Although the third point may seem a little fuzzy, it can be easily observed on sight, especially in the case of poster presentations.