✔ 最佳答案
Actually, there are some gramatical mistakes (not just the bracket) in the sentences. Since the backgroud of your case is not clear, therefore, some words may not fit the meanings.
- I'm afraid we never producing (these/such???) goods.
**** I'm afraid --> We sure/ promise
**** producing --> produce
**** (these/ such) goods --> the goods which you mentioned
- It (costs only/only costs) 5% more than the old one.
**** costs only
**** more --> higher
- 11st/11th???
**** 11th
- A comparison of the quality of our products with that rival ones will show you that ours (is/are???) far more superior.
**** (suggestion):- We assure you that the quality of our products are the best among the producers in this industry.
- It's the excellent quality that makes it worth the (difference in price/price difference???).
**** (suggestion):- You can have the excellent quality of the goods by just spending a little bit more.
- we have no other choice (to???) give up the deal.
**** (I don't know your meaning indeed) Using "to" is OK in this sentence!
Good Luck