If a buyer has 5 6bit-cents and double-pays 4 6bit cents for 8 products, all second transactions will be considerd invalid,
You'll get 4 double-spending points, making you an unreliable costumer and because so many mini-transactions have been made,
you can't spend your last 6bit cent until both you and the new seller are then focrced to use 7bit transactions.
Thus you'll have 2 7bit cents, which is worth 1 6bit cent. You cannot double your money by spending small amounts of it!

Thanks for your criticism!