Can I show the price including VAT for retail customers and excluding VAT for registered customers?
You can do this by going to 'Settings | Site Options | Layouts tab | Product group' and set the 'Price Layout' to 'Standard Tax Inclusive' (for retail customers) and the 'Price Layout for Online Customer Prices' to 'Standard Tax Exclusive' (for registered customers).
You can do this by going to 'Settings | Site Options | Layouts tab | Product group' and set the 'Price Layout' to 'Standard Tax Inclusive' (for retail customers) and the 'Price Layout for Online Customer Prices' to 'Standard Tax Exclusive' (for registered customers).