I'm the lead of the Future Future League (our internal Standard playtesting), and I make the final balance calls for our Standard-legal sets
In short, whether it is suitable for PSA is easier to judge if you think not just about whether it is an expensive card, but whether it is a genre that is easily compared or where condition differences are reflected in the price
A permanent that doesn't have any abilities, like a Gigantosaurus or Fortress Crab is called "Vanilla"
A security guard mentioned that he hadnt even heard of trading card games in years, having last played Pokmon and Yu-Gi-Oh
For most collectors today, buying singles is more cost-efficient than sealed product
Mew ex, for example, has a powerful attack that allows it to copy a move from the opponent's Active Pokmon, essentially making it the perfect counter to just about any deck