For those selling to members in the United Kingdom, please read the information below. You can bet that Royal Mail will also be looking to make sure that the items were legally shipped and proper postage paid.
From stamps.com:
Effective Jan 1, 2021, value added tax (VAT) must be collected for all goods entering the United Kingdom (UK).
There will be a 20% VAT rate on goods valued up to £135 (about $180 USD), which you must collect unless your online marketplace (e.g. eBay, Amazon, Etsy, etc.) is already collecting it. Current procedures for goods valued over £135 remain the same.
To prevent your UK shipments from being delayed, held, or returned by UK customs in 2021, please take the following steps:
1. Register for a VAT number with the UK: https://www.gov.uk/vat-registration
2. Collect VAT at the time of purchase.
3. Make quarterly VAT return payments to the UK.
In addition, you should include your VAT number on your customs declarations. This process will vary depending on your shipping software, so be on the lookout for instructions early next year.