I recently started playing Texas Holdem, and I found out I am quite good at it. Using simple statistics, you can determine what the top hand is, and thus get an idea of whether or not your hand is any good or if someone else is bluffing.
4 of a Kind and a Full House:
In order for anyone to have 4 of a kind or a full house, there must be a pair on the Board. Thus, without a pair the highest possible hands are a flush followed by a straight, and finally 3 of a kind.
A flush requires three cards of the same suite on the board. If no pairs and no three cards of the same suite are on the board, the highest possible hand is three of a kind.
Straight Flush and Royal Flush:
A straight flush would require 3 cards of the same suite on the board that can be sequenced with the cards in someone's hands. For example, the 3, 9, and King of the same suite is on the board and the other two cards are of a different suite, no straight flush is possible. A royal flush would require three royals of the same suite on the board.
Three numbers have to be available that can be sequenced with the cards in one's hand. For example, 3, 6, 9, Q, A on the board would make a straight impossible.
In summary there is always a chance someone has a three of a kind, but it can be mathematically impossible to have anything higher.
I hope this helps!