同意陈根花老师的解答，我在 Collins COBUILD English Grammar 找到了类似的观点：

should think it’s going to rain soon. 我想可能马上要下雨了。

I should think Sarah and Greg will be going to the party. 我觉得萨拉和格雷格会来参加聚会。

We'll need about 20 chairs, I should think. 我看我们需要大约 20 把椅子。

以上“should think”类似于“should like/would like”

【1】should 与第一人称连用，表示对某事没有把握会，可能(英语解释： You use should in expressions such as I should think and I should imagine to indicate that you think something is true but you are not sure.)

I should think it's going to rain soon想可能马上要下雨了。

'I suppose that was the right thing to do.' — 'I should imagine so.'

“我认为那样做是对的。”——“我想是吧。”

【2】 should 与第一人称连用表示客气的请求等想要，将会 (英文解释：You use should in expressions such as I should like and I should be happy to show politeness when you are saying what you want to do, or when you are requesting, offering, or accepting something.）

I should like to call my lawyer.我希望给我的律师打个电话。

We should be grateful for your help.对您的帮助我会非常感激。

I should be happy if you would bring them this evening.

如果今晚你将他们带来的话，我会很高兴。

'I should like to know anything you can tell me,' said Kendal

“只要是你能告诉我的，我都会洗耳恭听，”肯德尔说。