People are being advised by the European Consumer Centre to do their homework before buying something online from the UK.
The Centre says it has received over 400 complaints since January 1st about hidden costs such as tax and customs duties.
It says the problem has been made more difficult with the UK now outside the EU - which means refunds aren't guaranteed.
Dr Cyril Sullivan from the group says consumers should check the new rules on UK-based sites before making online payments.
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