The Dutch law is clear when it comes to online sales. As the exact legal information on the government site is pointing to an easy to read and understand consumer site, we do the same go here
On top of that, for clarity, visualcoach likes to explain the special rules for downloadable content:
As a main rule you can in most cases undo a buy with in 14 days.
If you buy downloadable software or get access to a video movie that has some kind of a protection key then you can't undo the buy. Just like you can't take back fruit to the market. I hope you can see why, for fruit food safety, freshness, storage temperature, etc. plays a role. For software we can't make sure you uninstalled particular software or did not look at footage.
So if you are afraid of making a stupid buy, make sure you inform yourself well. Ask for a skype meeting with demo, look at YouTube instructions, read the blog. This will reduce the chance you waist your money.