[yuriyuri]

It's been a while since I tried to write out an answer to a Japanese question so I hope I don't make any mistakes...
I'm sure I will be corrected if I am wrong though

Originally Posted by jesselt

危なさそうです ×　OR　危なそうです　〇

If you want to say something looks dangerous, you should use 危なそう
This is because なさそう is used for negatives, for example 危なくなさそう
The exception to this is the adjective いい
When saying something looks いい, the いい must change to よい and then to よさそう

I found this question on 知恵袋 which goes more in depth on the subject in case you are interested:
どちらが正しいと思われますか？？ 「〜なそう・〜なさそう」の使い分けについてで... - Yahoo!知恵袋

Originally Posted by jesselt

I heard it was dangerous
危ないそうです 〇

I does not look dangerous
危なくなさそうです 〇

I heard it was not dangerous
危なくないそうです 〇

They look fine to me...

Originally Posted by jesselt

I did not hear it was dangerous
危ないそうじゃないです

I haven't heard or read this myself so I don't know if people would actually say ～そうじゃない like this.
But the first thing I thought of when I read "Did not hear" was　～聞いてなかった or ～聞いてない depending on the tense of your sentence.
For example: 雨が降るなんて聞いてなかった

Hopefully my post helps you.
I'm sure if I made any mistakes somebody will point them out.