Gonzalo,

     You have a good beginning.  In the introduction,you wrote,"These issues are changing the consumer psychology."  You may need to provide more information on this, like 'why'.
     When you wrote, "There are many difficulties that millions of firms face when trying to implement a profitable e-commerce site."  I wanted to know more about the difficulties but it may not be important here, what do you think?
     In the section on constraint and barriers, you start off with two sentences talking about the positives and then you go into the actual constraints, I think that you could move the two sentences somewhere else.

     The 2nd section has good flow and moves well from paragraph to paragraph.

     This sentence, "There are many traps that managers should be aware to avoid while developing the e-commerce strategy." might sound better as, there are many traps that managers should avoid...

Gon-your paper is organized and your headings seem to fit well. It was well written and interesting, great job!

                                         Betsy