Which of the following should not be used as a guideline for making a purchase?
a. you budgeted for it.
b. you can afford it.
c. you need it.
d. you want it.

I think that you should not be buying things just because you can afford them - the correct answer is b).

If you budgeted for them, this means you decided that you need it, so all the options a) c) and d) mean that there is some kind of need for this object.

option b) does not say anything about your satisfaction with the project. So, if you are bold, you should not be buying shampoo even if you can afford it