翻译："如果你卖很多的话，我们可以给你打九折.“
If you buy a great deal of these products ,we can make a 10% discount for you.
或者:
If you buy in bulk ,we can give you 10% off(make a 10% discount for you).
个人认为后者比较好(因为前者用a great deal of /much/ many products 没有将"买很多 "表达得很清晰,正规.