answer: Mr. Thou worked out the offers and tells #Person1# some information about it. Also, Mr. Thou says that the offer remains valid for 4 days.
documents: #Person1#: Have you worked out the offers. Mr. Thou?
  #Person2#: Yes, we have. Here's our CIF quotation sheet. Please have a careful look.
  #Person1#: Are the prices on the list firm offers?
  #Person2#: Yes. All the quotations on the list are subject to our final confirmation.
  #Person1#: I wonder whether there are any changes in your prices.
  #Person2#: All these products are our best-selling lines. The prices of our products will change according to that of the international market demand. And we are always open to negotiate, especially on larger orders. What do you have in mind?
  #Person1#: How long does your offer remain valid? I need some time to get my supervisors on board with this plan.
  #Person2#: I understand. Our offer remains open for 4 days.