Personally, foreign regulations are not something I would spend time on until I start getting traction from the relevant country, otherwise it's a real rabbit hole.
And even if the seller is based inside the EU they don't necessarily need to care about VAT - the limit is around 100k EUR yearly revenue (varies by state).
Yes, but... there is usually some "processing fee" for the customer when it is done this way, so it depends on what they are selling. For instance, if they are selling $10000 items, then yes, the customer probably won't mind too much a $30 processing fee additional to a VAT of about $2000. However, if they are selling $5 items, the post office will still ask its $30 processing fee, even if the VAT is only $1... And, the customer will scream murder, refuse the parcel, etc.