to be taken in

• 不能上当

  cannot be taken in

• 我上当了。

  I've been had!

• 他不会上当。

  He will not be taken in.

• 当心别上当。

  Take care not to get fooled.

• 不能让同志们上当

  cannot let comrades be taken in

• 如果我们丧失警惕性，那就会上大当，吃大亏。

  If we let our guard down we will be taken in in a big way and lose out.