So what do you think?, how do other players know when I have good cards when playing online?
Depends on your call.
Since you are up against experienced online players, they are somehow used to determining what's on the mind of their opponent. But remember that it's about only their instinct and if you eat the bait, they will assume things that are currently on your mind. Anyway, just keep up with the others as possible as you can while playing online, and don't mind how they will know your next move. Instead, think of how will you determine their next move. Counter them with your strategy.