In the case of the ink cartridges I believe I was misled.
Many casual shoppers would not look any further than the price, why would you in these days of global trade
At one time there was a loophole in the law (which I believe has changed) which said goods of below a certain value (I think it was £15) were exempt from UK VAT.
This gave rise to a number of "off shore" retailers based in the Channel Islands and the Isle of Man who supplied memory cards and other small items at bargain prices. This may account for your consignment being split into a number of separate deliveries. I notice recently that there are a number of similar sellers based within the EU that seem to offer similar deals.
In my business, if I purchase an item within the EU, the seller does not charge me VAT, but I have to declare the item on my VAT return and pay UK VAT at the prevailing rate (currently 20%) on that item. Smilarly if I sell within the EU I do not charge the buyer VAT, and I presume the EU buyer is subject to the same VAT requirements as myself.
On the HMRC site it is stated that the UK has VAT "arrangements" with certain overseas companies, but there does not appear to be a list of who those companies are, or even what the so-called "arrangements" are.
I have purchased "grey" imports from several of the companies mentioned here, and the savings are much more than you save by using any UK "cashback" offer.
All the discussion here seems to be centred on tax savings, but there must also be a saving on dealer markup, and the commission paid to the Official Importer for their after sales support.
I have noticed recently that Panamoz in particular, have increased their prices considerably, and in some cases are actually higher than some UK dealer prices - so check carefully, an import is not automatically cheaper than a local retailer.