Everyone can submit a customs declaration themselves, but it is best to leave it to a specialist. After all, when preparing a customs declaration you have to take into account many obligations, special cases and exceptions. That’s why there are organisations specialised in this, who can act as a representative; the customs agent. Often when afterwards it turns out that the declaration was incorrect, there is discussion regarding the responsibilities of the various parties involved. Try to pre-empt this by making clear agreements.