As of writing this post no-one knows what the situation is going to be after October 31st for goods sent from UK to the EU as we do not know if the UK is actually going to leave on that date or if there will be a transition period if it does.
Assuming the UK leaves with no transition period, EU countries will be treated as non-EU countries are now: – prices charged will be net of VAT and any duty, import or sales tax/VAT will be the responsibility of the purchaser.
To this end I will be stopping sales to EU countries on 28th October until November 1st. The reasoning is two-fold; first it allows me time to reconfigure my shopping cart to correctly charge EU customers net of VAT and second and more importantly it will minimise the risk of EU customers potentially being charged twice for VAT. While it should only take 24 hours for an order dispatched from the UK to arrive in most EU countries’ customs systems, if you bought and paid on October 30th and for some reason the parcel did not arrive in the destination country before 11pm (?) October 31st the Customs authority of the destination country may charge you import duty and VAT as UK will no longer be a member of the EU, and by extension the Customs Union.
Obviously I hope to have more information well before my cut-off date and personally hope there will be a transition period as agreed in the original Withdrawal Agreement.