One of the agreements is the avoidance of double taxation. In other words, you should not pay VAT in the UK and in an EU country at the same time on the same item.
Exactly. Which is why, if you purchase from a EU country, you can ask the UK-based seller not to levy UK VAT, since you'll pay VAT in the EU.
From there on we have PERSONAL LUGGAGE delivery. This is not about trading abroad. This is the loophole.
It's fraud. Minor, somewhat understandable and in the large scheme of things rather insignificant. But if you think that what you're doing is somehow a legally permissible exception, you're just fooling yourself. It's only a 'loophole' insofar as you've found a courier that's willing to facilitate a fraudulent transaction.
Again, I'm not here to wave a finger, being moralistic etc. By all means, do as you please.
Here's a relevant excerpt from
a Dutch government website:
If I’m in the Netherlands, can I still purchase items from the UK online after Brexit?
Yes, you can. However, you will have to pay value-added tax (VAT) on (online) products. You will also need to pay import duties if products cost more than €150. Please keep that in mind, to avoid unexpected surprises.
Note that the €150 limit is EU-wide, as is the €22 small-purchase threshold below which you're not required to pay any VAT (note that this includes item price + shipping & handling costs; the total must not exceed €22).
This is from
the UK government:
3. Sending goods from Great Britain to the EU
Sales to EU business customers (previously known as dispatches) will become exports. For VAT purposes, the supply will continue to be zero-rated and evidence of the movement must be kept by the seller. There will be changes to the reporting requirements for these supplies.
Sales to EU consumers will also become exports, following the same general rules as for business customers.
Note the 'zero-rated' since VAT must be paid in the EU country from where the UK-originated purchase is performed.
From
the EU:
When you buy online from a non-EU country, VAT must also be paid, just as if you ordered goods that are already located within the EU. The VAT is either paid at the point of purchase on the website (for example, when you buy from a seller who is registered to use the Import One Stop Shop for VAT), or the postal operator or courier may collect the VAT from you on delivery.
Note that paying VAT at the point of purchase is only possible if the seller is registered with the One Stop Shop program, which involves VAT being levied by the seller
and paid to the EU country's VAT office they're registered with. Frame24 is to the best of my knowledge not registered with this program, nor has it otherwise any arrangement with an EU-based tax authority that involves Frame24 being able to levy EU VAT. Such custom arrangements are complicated to put into place and to administer and therefore well out of reach of a modest business like Frame24. That's what the One Stop Shop program is there for, but so far, it's mostly larger operations (e.g. AliExpress) that appear to participate in this.
If you desire more sources; here's a good one:
https://commission.europa.eu/system/files/2021-01/vat-goods_en.pdf
It details the EU-UK tax arrangements, which for all intents and purposes boil down to "importing from the UK is subject to the same rules as importing from any other non-EU country". It also details the sub-€150 limit and the One Stop Shop arrangement, which don't apply for Frame24 when buying bulk 400ft and larger bulk rolls, since these are valued considerably higher than €150 and Frame24 does not use OSS.