The ratings are comprised of a lot of different categories. Finishing, shot power, crossing, short passing, long passing, tackling, positioning, speed and stamina are just a few of the categories. Each player is rated on a scale of 1-99 in each of these areas which contribute to a players rating. Different stats are more important based on a given position.
Players are rated on multiple skill sets, with a maximum score of 99 for any given stat.
Examples of skills include Heading, Finishing, sprint speed, ball control, free kick accuracy, endurance, etc, etc, etc. There's something like 20+ skills you get rated on, supposedly based on real world performances.
Through some mysterious algorithm, EA averages these scores into an overall score, where 99 is again the highest possible rating.
Being in the 90s is very rare, and high 80's is considered world class. Most average MLS players are rated in the high 60s to low 70s, while most EPL players are rated in the mid 70s to the low 80s.
At that level, I'm not sure. I know there's some amount of local scouting done, but I don't think it's done based on the numbers of Fifa 16 coins. A lot more of it is done to make the players "feel" right, which is why you'll see certain teams' players be overrated (teams that win) while others are underrated (teams that lose).
Fifa needs to start making tendencies for players. Everyone plays the same. The only difference is if a player is better or has a higher ball skill rating. Every time I play against messi he is absolutely gone the entire match.
I don't think any player can be rated based on 3-7 games at the World Cup. Klingenberg is pretty consistent for club, but it's not clear if that information is being used for these ratings.
Kling did amazing in the World Cup go Watch the 2012 Olympics again and see if O'Hara ever cleared a ball with purpose. Klingenberg scored two badass goals leading up to the world cup and she provided much more to the attack than O'Hara ever did from that position.