Any of the following behaviours should raise concerns that the person you are interacting with is a scammer:
If you do come into contact with someone who is living in another city and can't afford a plane ticket to visit, consider your options carefully. We advise that you never send money to anyone you have met online. If you have been in touch on email and phone, and you would really like to meet, we suggest you meet somewhere neutral or else if you are prepared to take a chance and meet someone in another state or city, visit them and pay your own way. Never send money to anyone that wants to visit you.
Beware of any mention of financial difficulty and the need or request for financial assistance. This can come in the form of requests for money to pay for a visa, an airfare or to help a sick relative, or asking for your personal or financial details. Beware of anyone asking you to use a wire transfer service.
These are always scams. Always. Check Scamwatch for more details and examples. This includes emails requesting your account details so transfers can be made, and emails announcing that you've won a lottery or cash prize.
Are they young and good looking or out of your specified age requirements? This could be suspect.
If someone you are in contact with starts declaring their love for you within a matter of weeks (or even days), be cautious. The emails may be long and romantic, so be careful to use your best judgement. If you are unsure, get a second opinion from a friend or suggest a phone call with them to help you make a decision about this person's intentions.