How can a Collier County, FL board do a background check on foreign buyers?

How can we do a background check on some one who is NOT a US citizen  and does NOT have a social security number?

We have a unit owner who wishes to sell her condo to a couple from another country.

The couple does not live in the United States, do not speak English, do not have a social security number. We don't know how we can do a criminal and financial background check on this couple. This is required before we can approval any sale or any tenant in our development.

We don't want to block the sale, but we do want to stay in compliance with our own screening requirements.

What can we do?               

Steve