For the most part you can recognize cattle that have never seen people. I have come home with wreckless cattle a few times, and they went back. The problem there is the time and effort you spend rounding them back up. But, if you buy enough, you will eventually wind up with one that you wish you hadn't bought. The difference with sale barn cattle is price of course.
Heifers are something that can be difficult. There is no developed udder and no real track record. That is where ear adds value in my book. If she has lots of ear, she'll likely make an excellent cow. Hopefully you are picking up a terminal gal that cannot be bred back to her grandsire, so she is being sold.