" I had to pay import duty, VAT, and an admin fee to the courier (which outstripped the taxes). All in, I ended up paying more than just buying from a UK retailer."
That doesn't apply if you buy from inside the EU (My UK-spec FritzBox came from France, with french VAT paid, at 30% less than local pricing)
The non-EU sellers of these devices make it perfectly clear in their sales conditions that the buyers are responsible for all customs and handling fees. Anyone who buys from such suppliers had better make sure their ducks are all in a row as far as pricing goes(*), because if the customs boys spot a heavy sender underdeclaring values then they'll make sure all shipments get checked for a while.
(*) make sure that the price + shipping + vat + handling fee is still cheaper than buying locally - and don't send such stuff via Royal Snail or Parcelfarce as their handling fees are extortionate(**))
(**) UPS or Fedex cost more, but their handling fees are quite low (starting at less than 2 pounds or 10% of the VAT charge, whichever is higher, with a fee cap too)
Some handlers take the utter proverbial: About a decade ago I was stung by customs handling fees when we sent a suitcase from Bangkok to Amsterdam (overweight, containing various personal possessions). The dutch outfit which received it wanted in excess of 500euro to release the case, so we told them to burn it as it was more expensive than replacing the stuff.