Writing Feedback / GRE argument: sales prediction [2]

In sum, the author wants to make a prediction about the future sales whereas his deduction contains several facets that are questionable. However, if the author can provide a more convincing study to investigate the players' preference, at the same time, doing a more in-depth investigation of factors which can effectaffect the products' ? sales, the prediction would be relatively strengthened.

More than half of your sentences are negative. Please rephrase.
You should replace some repeated words.