This has "bad idea" written all over it. In fact I am not even sure where to start the analysis. My suggestion is to not assist in shipping the cars, do not accept the cashier's check (you assume it might clear the bank) and clearly do not double cross the export company. Those companies are often tied to organized crime. Best thing to do is find another occupation.
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Given your set of facts, you could be liable to the Export Company for conversion or fraud, given that you took a vehicle they intended to sell and sold it for your own monetary benefit. If you've got issues with how this company operates and have ideas of "whistleblowing" for profit, think again. Very few "whistleblowing" complaints to regulators or gov't authorities see the light of day. Even if they do, there is no guarantee that you'll receive anything.
Your course of action doesn't sound prudent to me.
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I agree with the prior attorneys and would add that often times anything to do with a cashier's check form an overseas company involves fraud. Make sure you deposit the check and wait a few weeks to make sure it clears the bank.. Too often we see people depositing overseas cashiers checks in their account and then spending the money; the check turns out to be bogus and you bank expects you to make the money good. Just because your bank credits your account with the money does not mean the check is good and has cleared the sender's bank. It can take weeks for that to occur.
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If you cash their check, use their money, then you're part of their scheme and will be prosecuted equally, even if you "cooperate." If you believe they are conducting illegal activity you should report that to law enforcement. You would not be a buyer in good faith.