As a UK citizen resident in Ireland, the situation now for goods coming from the UK is an unmitigated disaster, as many UK sellers on places like E-Bay don't know the new rules, or are simply refusing to sell to Ireland at all.
Brexit is the reason, the system now is that a UK business seller should sell without adding UK VAT, and complete complex customs declaration paperwork with the relevant codes provided so that the EU authorities (not just Ireland, all of the EU) can then apply the relevant charges to import into the EU.
At one time, private individuals could ship GIFT items without additional charges, but even gift from family members can attract charges, depending on the value.
The first charge is VAT, which is for goods to Ireland usually 23%, but a few items may be at a lower rate, or even fewer are zero rated. There is no exempt value now, until recently, items under (I think) €23 were not charged, but that exemption has now gone.
The next issue is that some items above €150 can also attract customs duty, at varying rates depending on the product, and that's why the tariff code is all about, and if that's not there, or wrong, the items could well be returned to sender.
The charges will also be worked out on the inclusive value including shipping charges, which adds to the final bill, and then to add insult to injury, the couriers are adding a (sometimes substantial) processing charge to the final bill for their handling, and possibly payments made to get the item into the country. Don't even then start on the delays that this process is causing, that's another issue that's causing huge problems for many companies.
The result is that an item that initially appeared to be cheap can end up costing a lot more (close to double in some cases) than was expected by the time it is delivered to the end customer, and yes, that's what the UK voted for.
I can tell you that in a while, it will become clear just how big a distaster it will turn out to be, it will take a while, but there will be massive changes from some companies who will decide that the complexities of dealing with what has become a third country for tax and VAT are not worth the hassles, and they will move to alternative suppliers within the EU. It's happening already, the number of companies that no longer ship via the UK, and are using more expensive and longer freight routes to France to avoid the paperwork minefield and attendant delays is only massive, and that's only the start of it.
I'm no longer buying on E-Bay, it's a pain to have to use EU web sites, but the costs are so much cheaper, and the same is true for Amazon, for the same reasons, there are so many suppliers on both platforms that just plain refuse to ship to Ireland, it's not worth wasting the time looking for people that will ship "abroad".
Maybe UK suppliers will cop on, and get organised to send goods to the EU, there are some in the hobby that are organised, but there's way too many who need to get their act together if they want to survive, unless they're happy to only supply UK customers.