I've been silent on this for way too long. I play a fair deal of Words With Friends.
1. Your Every Move Is Perfect
Making perfect moves every turn is statistically impossible in this game. There have been turns I've gotten nothing but consonants and nothing but vowels. In any given game there's a chance you'll get a hand like that and there's usually nothing to do but play a crappy 3 letter word and hope you get some vowels or consonants in your next turn. However in the wacky world of words there are options if your vocabulary is large enough. But the only way the average person is going to know where to place them is using a site like this. I know they exist. I just don't use them.
2. I Know You Personally
There's a random player option in the game. I've used it a total of once. The person I did pick up doing that is an pretty good player too. The rest of you guys I know personally and some of the words you're using have never ever come up in regular conversation. I've seen your Facebook posts. I've went to school with a number of you. I'm not implying you don't have a large vocabulary. Just that next time we talk feel free to dazzle me with it. :)
3. It Takes You A While
If I'm really into playing a game (and you are too) I play within a minute of getting a turn. Sometimes I'll take longer because I'm REALLY having trouble trying to form at least one viable word from the tiles I got. However, I notice when after every turn I play it takes you 5 minutes to return and in which case refer to item1.
4. You're Greedy
This is the biggest telltale on the list. Anagram solvers and scrabble cheating sites give you all the viable options given the nature of the space you want to play in. Now lets say you have IASHTEZ. Now you could easily spell "haze" or "size" and not rouse my suspicion. However there is a 7 letter combo for this word and it's "haziest". But you probably didn't see that right off the bat. It turned up at the top of your word search and it's worth a bingo bonus.
Another good one is playing more letters than they really needed to play. An example is playing "embolden" instead of just "bold".
Now if you play the game straight, well bravo for you. If you cheat, then so be it. See even though I took the time to write a lengthy blog article on cheating in Words With Friends it doesn't affect my decision on whether I enjoy playing the game or not. In fact, I often welcome the challenge. Granted, at least 90% of the time the computer is going to beat me...but by how much? I don't mind coming in a close second to a machine that's capable of absolutely decimating me depending on how I play. It only makes me a better player in the long run. BTW, you guys really shouldn't be teaching me these words. They WILL come back to haunt you. ;)