How to Handle Big Order Bargaining

It is almost the end of this year. Are you all struggling for this year to facilitate cooperation? But what if the customers ask for a lower price with big order?
I have a friend named K who had worked in the company as a foreign trader for 2 years and she was worring that she couldn't get a big order. And then the other day, she got a good news that one customer in germany gave a big order. I was so glad to hear that here came a positive unintended consequence while K was not so happy as I imagined. She worried if the customer would ask for a lower price. Because when it came to the sample, the customer was unwilling to pay full price of the samples but half price. She had no idea if this customer was reliable or not.
I understand after all we all encountered such situation when the customer gave a great order but then a smaller one. So what can we do to avoid such consequence?
1.Before bargaining, ask the customers if they are sure about the order quantity.
We can emphasize the cost of production processes and refer to our low profit to make them realize although it is a big order but there is no room for price reduction.
2.Technigues in offer
During an offer, we can prescribe a limit to note the period of validity to let them know and we can also make some adjustments on accessories.
3.Underline the limited order quantity to get the maximum discount on purchasing raw materials.
If the customers want a lower price, before the concession, we should let them know the supplier get a big discount through large numbers of purchase of raw material and if the order is smaller, they won't get a discount.
Where there is a will, there is a way. I hope you all can make good fortune in the next busy season.