How can you tell if someone is a child molester?

Essentially, you can't. Child molesters are effective con-men, if they gave away lots of signals they wouldn't get very far. For this reason most lists of warning signs are overly generalized. However, sexual abuse organisation 'Stop It Now' marks out some features to look out for.
- Lack of adherence to boundaries of personal space with children.
- Secret interactions with children
- Sharing of inappropriate personal or emotion details with children
- Inappropriate sexual comments or interest in childs sexuality or sexual development.(repeatedly talking about a childs developing body and in older children specific interest in their dating and sexual experience)

Essentially, you can't. Child molesters are quite crafty and effective con-men, if they gave away lots of signals they wouldn't get very far. For this reason most lists of warning signs are overly generalized. However, sexual abuse organisation 'Stop It Now' marks out some features to look out for.
- Lack of adherence to boundaries of personal space with children.
- Secret interactions with children
- Sharing of inappropriate personal or emotion details with children
- Inappropriate sexual comments or interest in childs sexuality or sexual development.(repeatedly talking about a childs developing body and in older children specific interest in their dating and sexual experience)

With great difficulty as they are very crafty. Most child molesters are apparantly known to the molested child or  their family. They are like vultures. Just awaiting their chances.