Yes, it is! It sometimes happens that customs has to estimate the actual value of your package. In that case it can sometimes go wrong. It is also possible that you send your parcel back to the sender. In that case you can also object and reclaim the customs clearance costs. You can do this at the mail order company, or directly at customs. Make sure you have all the necessary documents. You cannot simply ask for a refund without proof of purchase or proof of return.