Multiple regression with negative coefficient for Sales vs Revenue

Hi I have a table of data with 3 columns: Sales,Cancels and Net revenue. I am triying to perform a Linear regression to check how much the sales and cancels affect the Net Rev but the first thing i noticed is that there is a negative correlation between sales and Net revenue (So the less I sell the more I gain?) Corr(Sales,Net Rev)~-.68

These are monthly time series, where sales and cancels are dollars per month and the net revenue is '000 dollars per month. The revenue is the sum of different incomes but not directly the sum of the sales. Then I run a linear regression net revenue v.s sales and Cancels (Using Excel) and I see that sales is significant at 99% but again it has a negative coefficient.

So my questions are:

1)Why do I get this negative correlation between sales and revenue? I supposed is an Spurious Correlation. 2)Is there some transformation I can apply to data to get better results? 3)How do I intepret a negative coefficient between sales and revenue?