Expressing "Fair enough"
Essentially it's form of concession, either through a counterargument or the acquiesence of a mutually agreed upon opinion. 

There are different ways to express concession in Chinese. Here are some possible translations that I can think of based on your examples. This is far from exhaustive and some of them might be preferred over others depending on the situation and context:

Bro A: 兄弟, 你为啥没要那工作? 有这么多的员工津贴! 
Bro B: 是啊，但这种工资水平还不够贴补我汽油费用的. 
Bro A: 嗯，　有道理．

Bill: 你真不该喝这么多，　太伤肝脏了. 
Jill: 你不也每天吸一包烟吗？ 
Bill: (你)说得对.


Here are some others: 合乎情理，　说得通,　说得过去，　(我)认了.

In the first example, Bro A has taken into account the additional information supplied by Bro B and has modified his previous conclusion. In this case, he's cooperating with Bro B so any reply that states 'your reasoning is sound' is suitable. This includes 有道理, 合乎情理, 说得通, 说得过去 and possibly 可能是吧 (which shows more doubts than the previous examples). 

In the second example, Bill makes concession, due to his argument being countered by Jill. In this case, he's not cooperating with Jill, but acknowledging Jill's point/his defeat. So 说得对 is probably the best answer out of the list. 好吧 is appropriate, but it only serves as a precursor to what follows. One possible reply is 好吧, 我认输了. This particular reply is probably more appropriate after a long-winded argument with a lot of toing and froing.