In what ways do professional and casual players differ when playing Scrabble?

Besides the obvious” knowing more words,” three main things separate an expert from casual players. Every turn in Scrabble is a puzzle. Your “goal” is to find the best play every time, more or less, and expert players can usually find the best-valuated space on almost every turn.
The second is expert players have memorized dozens or hundreds of potential bingo words, and they are actively scanning the board for bingo opportunities on every turn. Most casual Scrabble players view bingo as a rare accomplishment, something you might aspire to achieve once or even twice in a game. Still, every turn is potentially about bingo for serious players, and because of the time they have spent studying the Scrabble dictionary, they are brilliant at scoring them.
The last prominent example is what you do in the endgame and the pre-endgame. Unofficially, the “pre-endgame” is when seven or fewer tiles are in the bag, so you can’t exchange. Tournament players often track tiles during the game, and by this point, you will have a good idea of what your opponent is likely to have.
Often, casual players just coast through an endgame by focusing on getting rid of as many tiles as possible and scoring reasonably well. Most importantly, experts will try to be creative to steal games and are very obsessed with “optimizing” their game.