About the Thesis Statement~

This essay provides a list of issues that a consumer needs to consider before deciding to extend a product warranty.
1.我不觉得aim用在这里很合适,又想不出更合适的,干脆不用.
2.consideration和decide都是consumer要做的,before引导的状语也是修饰consideration的,而不是修饰主句谓语的.所以显然consideration要变成一个从句里的动词.
3.很自然的,从句是一个定语从句,要修饰的是这个定语从句的宾语,也就是要考虑的问题,英语是issues.
4.consumer用单数比较好.
5.warranty也要有冠词.我又加了product使表达更清晰.
最后,再化简一下：
This essay discusses the issues that a consumer needs to consider before deciding to extend a product warranty.
补充：
如果是引言的最后一句,通常可以这么说：
In this essay,I will discuss a number of issues that a consumer must consider before deciding to extend a product warranty.
非要用目的的话,purpose也比aim好.aim有目标的意思,在这里不合适.
The purpose of this essay is to discuss the issues that a consumer needs to consider before deciding to extend a product warranty.