You do sometimes have to pay customs tax. Unless you are well connected or Qatari, I don't think there is much you can do if the paperwork is in order. Sometimes I have to pay something, sometimes not. One time when I was dealing with a cargo agent he told me the customs was 1000 and I asked why it was so much and he immediately reduced it to 200. But, when Aramex say I have to pay it, I just do