Question

各位英语大神又来看看我写的语法结构什么的有问题没？

This picture is for the purpose of illustrating the issue of stars’ honesty in reality.Then，let us closely observe it.In the cartoon ，there is a celebrity，standing in front of a video camera and claiming that he has tried the medicine.Meanwhile，we can notice that the manufacturer is paying for star’advertisement in secret manner.

Answer 1

您好，

This picture is for the purpose of illustrating the issue of stars' honesty in reality.
这里的 stars' honesty in reality 可能会导致误解，除非 stars 之前就已经有解释为（明星），in reality 可能改成 in the real world 更容易理解。

Then, let us closely observe it.
个人觉得把 Then 改成 Thus 可能更好些。

In the cartoon, there is a celebrity, standing in front of a video camera and claiming that he has tried the medicine.
语法没有问题。

Meanwhile, we can notice (that) the manufacturer is paying for star' advertisement in secret manner.
paying somebody (for) something 或是 paying something to somebody；secret 的形容词是 secretive；advertisemen 前面还可以添加 false（假的）；所以可以改成 .... is paying the star for the false advertisement in secretive manner.

Answer 2

第二句话，要斟酌一下。
in the cartoon做状语，standing 看着是缺少逻辑主语，应该加个主语在前面，stand改为做动词。
看出了这点有质疑，其它大底没错。