First thing I'd check is the numbers. First look at the dash VIN. Then look on the drivers side core support and the top of the drivers side cowl. Both should have the last 6 digits of the VIN stamped into them, and match the dash VIN. Of course those can be faked, but it's a good place to start. An authentic fender tag, door VIN tag, and broadcast sheet are added bonuses. If your comfortable that all of the above is legit, and checks out, proceed with the advise others have given you in this thread.

One last thing, and check it out FIRST. Make sure there's a good, clean, legit title.

GOOD LUCK!