The long and short of it, each EU member sets their own VAT and import tax rates you have to pay.
This is simply incorrect, have a think about it, how could the EU work if that were correct? Everything would enter where it was cheapest! That's the point of a trading block, standardisation. VAT varies, standard rate from 18 to 25%, but for online sales from July last year it's applicable at the consumers local rate rather than the retailers. Google IOSS if you'd like the full details.
My friends recently ordered some Austin parts from UK and these were sent via DHL who are the German Post parcel division. The UK vendor took off the 20% UK VAT when charging and DHL charged the local 19% VAT on delivery. The total VAT was less than EUR 6- and would have left the final price about the same after the transaction but the handling charge to process it was EUR 7.50. Other carriers (DPD, GLS, TNT, FedEX etc) are free to charge a less competitive rate if they handle the VAT processing. Same friend had to pay a EUR 40 handling fee on some 2nd hand parts that were not sent via DHL to Germany. In this case, the handling fee exceeded the cost of the shipment.
For larger platforms (Amazon/Ebay/Aliexpress etc) the VAT exchange on international transactions is often now built into their systems, so there is no processing fee when delivered. At least, that is my experience since Brexit.
I detailed the regulations upthread, member States can't vary them, consignment* under E150 the VAT has to be paid before Export, over that and it has to be paid after Import. If you've received goods over that value from outside the EU, then the supplier has set up a process where you're technically being supplied from within, also mentioned upthread.
If you friends have been billed for any additional cost on an order under E150, a mistake has been made and they should apply for a refund. There's been several stories in the UK press about such mistakes on goods sent from the UK to EU, so it is happening, but it shouldn't.
* That it's consignment value rather than the individual item values is important.