I feel i have been done wrong by TMR..

The story I'm about to tell does not reflect in anyway any purposely wrongdoing by TMR.
I have dealt with TMR in the past and although there was a glitch, they went out of their way to rectify it and all ended well; so, I know they are good guys that practice good business. However, the other day I purchased, and by purchase, I mean moved into a cart and then pressed the pay button for a pair of Gallo speakers. To my surprise I received an SMS saying my card was charged on the one hand, and at the same time I've received a Message that the speakers have already been sold to someone else. This is the short end of the story; the full story ‏shows up a few posts below. I admit at first I've been very upset and I started this post in a different way, it parked a lot of reaction, most of it in favor of TMR which I find to be great, but the real question I want to ask and this is regardless of if it happened with TMR or with any other venue, is,  how can it be that once you move any product into a cart and press the pay button within a few moments the product can be sold simultaneously to another buyer? isn't there any smarter way to prevent such an incident which is obviously going to leave one of the customers disappointed and upset?