我只是看看，不一定买？英语怎么说？

Just have a look.
在英语的口语中就跟我们中国人说话一样，越简单越好。

I'm just having a look

后面那句就不用翻译了 显得啰嗦

I just take a look,and there is no obligation to buy.

I'm just taking a look and I won't surely buy it(anything).

I just take a look, I am not sure if I will buy it or not.