Ryobi petrol lawn mouer

We bought a petrol Ryobi lawn mower, we used it not more than 10 times, when it stopped working we took it to makro where we bought it, as it is still under warranty, makro then sent it to Ryobi, they sent us a quotation and said that we have to pay as the carburetor seal is not covered, I asked, how could this have happened so they said that we should have emptied the petrol after use, now how can we empty the petrol if there is no facility to do so, Infact in order to empty the petrol 2 people have to turn the machine over which is not ergonomical. Also when we went to makro the sales consultant never explain this to us, so why is it our fault? and why should we pay? I spoke to a gentleman from Ryobi and told him I will take the matter further up and he didn't care