怎么觉得这个ivisa.com像个骗子网站？

They have the same rights as any US citizen, even when traveling outside the United States. Therefore any green card holder who plans to go to Mexico needs a valid passport from their country of origin. With your foreign passport plus the green card, you will be allowed to enter Mexico by air, sea or land.

不需要。但是墨西哥城海关查的比Cancun的严格，最好提前打印一下返程机票。上月底刚入境的墨西哥城，手机上出示了返程机票。

中国公民去墨西哥不需要visa, 只是回美国时要绿卡。