If the word is "questionable", then it should be resolved in a dictionary challenge, which is what the rules call for. Before play starts, you decide what your reference dictionary will be (Scabble publishes an official one, which is what is used in tournament play and anyone can get one if they want. It's handy, since all the things in a regular dictionary that are illegal Scrabble plays like proper nouns and so on are left out). If you think a guy's word isn't kosher, you can challenge it. If you can't find it in the dictionary, he picks up his tiles and loses his turn. Otherwise, the challenger loses his next turn.