At least in Germany (possibly also EU) when ordering something (excluding software, movies, food) online or via mail (i.e. not buying in a store) you have the right to send it back within two weeks without having to give a reason. This is to counteract the problem that you can try out a device in the store where you might buy it, but you cannot when ordering online. In any case, usage marks, like scratches, etc. just mean that you may not get a full refund.

Some retailers allow for longer periods; e.g. Amazon allows for a month instead of just two weeks.