Hi Lionel,
I am Dave, I will help you with this.
With those websites that sell Windows licences, it is very hard to judge whether they are selling genuine consumer Windows licences, really the only thing you can go by is the price they are charging, if the price is too cheap, then the deal is too good to be true.
That website you have mentioned indicate they are selling OEM (PC Manufacturers) licences, at a very cheap price, that would indicate that they are selling volume licence keys and honestly, you should be very careful, those licences will initially activate, but will soon after automatically deactivate when Windows cannot contact a company key management server to re-arm the licence.