I purchased a monitor during a promotion they were running. They cancelled the order stating "invalid credentials". Not only was the actual seller unaware of what that means, Rakuten's support had no clue either. Nevertheless, they pulled out the terms and conditions and stated that they won't fulfil the order.
To top it all up, a week later the amount is still blocked on my card.
Their website is terrible as well and the checkout procedure is bad to say the least. I'll keep to reputable sellers such as Amazon from now on, never again Rakuten. Avoid at all costs.