I noticed that when I was using this tool, the data in the tables would change, often by a lot (up to 50%) when I sorted the columns. (Did nothing else, just sorted.)
Since I was starting a new campaign and really needed data, I contacted Google about this and was told: "I understand that the estimates are changing in the Keyword Planner tool when you sort the data. I reproduced this on my end as well and was able to confirm that this is a known technical issue on our end." "Unfortunately the information in the Keyword Planner Tool is currently not the best source of data for your analysis."
They then went on to suggest I just test things blindly.
So, what do you do to get information about keyword traffic and ppc estimates?