Hi KZ,
The trader will have to pay customs charges due as per tariff, they need to speak to exporter or customs/tax authority of exporting country to see if they can zero rate the sales VAT because goods will be subject to import VAT as per tariff in UK.
If the importer is not VAT registered in UK then it is not possible to claim back the import VAT.
Please see step by step guide on importing goods into UK on below link:
Import goods into the UK: step by step
Thank you.