Translation:If there is no discount, I won't buy it.
It is more English though. Let's have the translations be as English as possible, shows the difference between typical English and typical Mandarin nicely
"if you don't give me a discount I won't buy it" was rejected, but I think it's fine [even though there is no "me" in the chinese, it's inferred..the effective meaning is the same]
But you can also be talking to a friend. This is usually not good wording for cutting the price. ;-)
"Sale" and "discount" mean the same thing. They should both be acceptable translations.
Not quite. You would have to say "If it's not on sale ..." The phrase "no sale" is something a salesman or negotiator would use and that has a different meaning.
Should also accept "If there's no discount I just wont buy it" as 就 can translate to "just" and this is the natural way I'd say it in English.
The translation for your sentence should be “如果没有打折，我[就是]不买。” — which seems contrived without knowing that “you” had once denied before and still insist — you could use 绝对 (definitely) instead regardless of the context — “…，我就绝对不买。”
I believe that "If it is not discounted, I will not buy it." should be accepted.
"打折" appears to be a verb like "打電話" (to call) and "打籃球" (to play basketball) that has been converted from a noun with the special verb "打".
就 means “then” in this sentence.
Even if 就 can mean “just”, it doesn't mean natives will naturally interpret it that way. “不管(no matter)有没有打折(have discount or not)，我就不买。” is a much better sentence for expressing that meaning.