I own an online shop and I'm trying to find the factors that would predict the profitability of a merchandise. To do this, I ran a linear regression with profit as the dependent variable. For the independent variables, I used all the data that I have recorded about each merchandise, which included things like the number of competitors, competitors' prices, year of production, etc. The idea is to create a list of criteria to determine if I should or should not sell a certain merchandise.
However, the result is always obvious: the selling price and buying cost are the only significant predictors (there are other statistically significant variables, but their beta is very low). Since they would obviously affect the profit, should I exclude them?
I did try to exclude them and the result is a lot more interesting, but I don't know if they are valid. I've also tried swapping the dependent variable from profit to the selling price and their results are identical.