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Scenario: I was going to buy two computers last week at my work place but I didn't. And someone says: Why didn't you buy your computers last week?

I answered:

What do these mean? If they are incorrect, why?
1. I didn't want to buy the computers and then return the products later. It would look bad for my store if I had done that.
2. I didn't want to buy the computers and then return the products later. It would look bad for my store if I did that. (Is this one better than #3 or #3 is better?? Because I never bought the products and I didn't do any returns? This is conditional #2 (Present Imaginary), does it mean returning products in general is bad? If so, I should use #3? or #1? to refer to my past?)

3. I didn't want to buy the computers and then return the products later. It would have looked bad for my store if I had done that.
4. I didn't want to buy the computers and then return the products later. It would have looked bad for my store if I did done that.

Thanks.
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Scenario: I was going to buy two computers last week at my work place but I didn't. And someone says: Why didn't you buy those [your] computers last week?

I answered:

What do these mean? If they are incorrect, why?

1. I didn't want to buy the computers and then return them later. [using 'the products' is okay too but I think it's more natural to opt for pronouns]. It would look bad for my store if I had done that.

OK

2. I didn't want to buy the computers and then return the products later. It would look bad for my store if I did that.

(Is this one better than #3 or IS #3 [is] better?? Because I never bought the products and I didn't do any returns? This is conditional #2 (Present Imaginary), does it mean returning products in general is bad? If so, I should use #3? or #1? to refer to my past?)

3. I didn't want to buy the computers and then return the products later. It would have looked bad for my store if I had done that.

JTT: Jack, what's the difference between,

1) I am 187 centimeters in height.

2) I grew 4 centimeters since my birthday.

4. *I didn't want to buy the computers and then return the products later. It would have looked bad for my store if I did done that.* THIS IS UNGRAMMATICAL
Comments  
Students: Are you brave enough to let our tutors analyse your pronunciation?
JTT: Jack, what's the difference between,

1) I am 187 centimeters in height.

2) I grew 4 centimeters since my birthday.

In #1 your telling me your height, you're 187 centimetres. In #2 you have grown 4 centimeters since your birthday, you're telling me how much you have grown.
4. *I didn't want to buy the computers and then return the products later. It would have looked bad for my store if I did done that.* THIS IS UNGRAMMATICAL


Sorry I meant this:
4. I didn't want to buy the computers and then return the products later. It would have looked bad for my store if I did that.
Read and think about what I've said in "Storytelling with Conditionals", Jack. Hopefully, then you'll be able to answer your own questions in this thread.

Then please do get back to us. Give it a whirl/go, Jack!!