I think another great idea would be to include interested and not interested buttons that could be sent in the messages as an option. It will allow users to quickly determine who is worth their time. This would take the form of a tab on the bottom toolbar in the direct messaging window. You would simply click it and it would send a prompt that would ask the question simply "interested -or- not interested". The recipient could click tap on either choice which would send a response to the sender that could be quickly reviewed so the sender would know if there were any point to proceed with the conversation.