Why some main dealer do not do tax free car sale ?

Actually, I went to Benzs main dealer today required a tax free car sale for exporting to hong kong, they said that they do not do it without any reason. In addition, the purchased of the new car will be exporting directly to HK without registering a UK owner.

I do not know why they do not allow me to pay the car price without vat even if i meet the following regulation. Could someone tell me where can i get a brand new car with tax free ?

In the HM custom rule, it said

The Personal Export Scheme (PES) allows entitled customers to purchase a motor
vehicle in the UK free of VAT for export outside the European Community. Subject to
some restrictions the vehicle may also be used for a limited period in the EC before
being finally exported to a destination outside the EC.

You can use the Scheme if you are:

(a) an Overseas visitor. This means that you have not been in the EC for more
than either:
• 365 days in the two years before the date when you apply to use the Scheme; or
• 1095 days in the six years before the date when you apply to use the Scheme;
and
• you intend to leave and remain outside the EC with the motor vehicle for a period
of at least six months; and
• you comply with all the other conditions of the Scheme.

(b) an Entitled EC resident. This means that you have been in the EC for more
than:
• 365 days in the two years before the date when you apply to use the Scheme; or
• 1095 days in the six years before the date when you apply to use the Scheme;
and
• you intend to leave and remain outside the EC with the motor vehicle for a period
of at least six months; and
• you comply with all the other conditions of the Scheme.