With bank deposits to pay product exhibition fees 10000 yuan, do accounting entries borrow: product cost of sales credit: bank deposits borrow why?

No. Cost of product sales is product-specific, i.e., expenditures directly related to the cost of the product.

Bank deposits to pay the product exhibition fees 10000 yuan, should be expensed as a period expense "selling expenses - publicity and exhibition costs"

Borrow: selling expenses - publicity and exhibition 10000

Credit: bank deposits 10000

I hope this helps!