First of all, it is next to impossible for fake items to get sold in Qatar. The authorities are always vigilant and keep an eye on such activities. Second, Carrefour is a r-e-p-u-t-e-d shopping place and surely they would not do something so unethical as to sell fake items or carry out fraudulent activities.
Having said that, there could be several other reasons why the salesman may not have been able to answer your query. Maybe you asked the wrong person and he may not be from that section. You could asked for the supervisor who could have helped answer your query. Secondly, one item item gets manufactured by different companies, have different brand names and carry different price tags. This applies to mobile phones, laptops, cooking oil, cheese, butter, apparel etc. to name a few. I am sure you are aware of this.
Rather than just jump up, draw negative conclusions and then post incorrect views at a website, you should have just sat down and given a cool thought. Try drinking some cold banana juice as it will help you from drawing such illogical conclusions.
Doha is getting a bit hot these day. It appears the heat is having some effect on your thinking power.