Selling faulty stuff and want to charge for it to be fixed

My son bought a Volkano Bazzoka (Bluetooth Speaker) worth R500 on 2 October 2018. The on/off switch was faulty as he couldnt turn it from on to off (it got stuck on "On" mode). When he tried to force it then it broke.

He went to CNA and they say its is a technical clique but he will have to pay R300 to get if fixed because it is now a physical damage. My question is: What should someone do when they are sold something that had a technical fault that will result to a physical damage? or was he expected to keep it on throughout? and why those technical glitches, if they are common, the customer is not informed of and be told what to do should it happen to avoid the physical damage as Clicks has made it clear that they wil;l not pay for the repair although they are aware that such problems occurs with these speakers?