Buy property from foreign seller with under market price?

[Steve Pin]

Scenario:  An off-market property owned by an foreign investor who's willing to offload it and quick sell with a way-under-market-price (in CA)

Question: Would there be any tax related or any risks involved if the selling price is, let's say, 40% or even 50% under market average for the same type of property?  

It's definitely a hard-to-find good deal, but I've never bought a property from a foreign seller before thus wanted to be extra cautious.  Greatly appreciate it if anyone could provide some advice here.  Thank you in advance!

Steve