The first time Walt sold Gus meth was toward the end of season 2 of Breaking Bad after they met in Los Pollos Hermanos. Guss trait as a careful man is highlighted several times. One example was his straight up refusal to even speak to Walt because he saw that Jesse was high. However, he goes on to do the transaction. Walt gets his money and Gus gets the meth. At this stage Gus didn't know Walt had a brother in-law in the DEA.
Then, in the final episode of season 2 Gus visits the DEA office as he's sponsoring a fun run. While in the office he spots a picture of Walter. He asks Hank who the picture is of and Hank explains that its his brother in-law.
The next time we see Gus is when Walt goes to Los Pollos Hermanos to tell him he's retiring. Gus straight out offers him 3 million (I believe? I need to check the figure) for 3 months work. I find it a bit hard to believe, seeing as how there was such emphasis on him being a careful man, that he would talk to him in this way the very next time he sees him after finding out about Hank.
Why did he take this action?