13. Our price is set according to the quantity.
我们根据数量定价。
还能这样说：
Our products are priced according to the quantity.
Our price is depending on quantity.
应用解析：
a quantity of 一些；
in large quantities 大量地，大批地
14. The price of our products is unified all over the country.
我们产品的价格是全国统一的。
还能这样说：
Our products are in the same price around the country.
Our products are set at the same price.
15. How do you sell the watermelons?
西瓜怎么卖？
还能这样说：
What price do you charge for the watermelons?
How much is the watermelon per half kilo?
谚语：
Cry up wine and sell vinegar.
挂羊头，卖狗肉。
16. Is there something cheap of this kind?
这一款有便宜的货没？
还能这样说：
Do you have any cheaper ones of this kind?
Is there something of this kind at a lower price?
17. The expensive goods are not all in good quality.
贵的商品质量不见得好。
还能这样说：
Not all the goods at a higher price have good quality.
Not all the dear goods' quality is fine.
应用解析：
have quality 质量好；
excellent quality 品质优良