Can the client be on site during product photography?

Today a potential customer came to Guangzhou photo studio to discuss a product shoot. This prospective client seems very special. He did not give us any details on the project before coming. For most customers, usually they ask for a quotation before the face-to-face meeting, by communicating the project and the image requirement first via email or phone or Skype etc. Only when both parties agree on the key points, it is time for a personal meeting to finalize all shooting details.
On the contrary, he came and showed us the products. Then he told me that actually he has his own studio in the company. They normally shoot all the items in house. Only because the new products (electronic cigarettes) from the new line are too difficult to take pictures due to the material (stainless steel), he must find a professional photographer to help him. I asked him about the budget. He replied “no budget limit”, but he has a special condition “I must be on site during the shooting to ensure accuracy and efficiency. I know many commercial photographers won’t accept my proposal, but I insist”.
Here is the key point: it is the industry practice that professional photographers will not allow others (including the clients) on site when they shoot products. Although this customer claimed he does not care about the price, I decline his project immediately.