Ddatabase performance for ecommerce solution

Hi friends 

When design database for ecommerce solution , we should performe correct normalization?

For example grid: we have two type of customer  ....> 1.supplier 2.customer 

For users , we can design  two tables : one  table  for customer and second for supplier .

But we should design one table and separate two customer with type or separate table because we have ecommerce solutions .

I have important question at last ? 

When you have ecommerce solutions , what's degree of transaction important? Normalization or transaction important?