So many different kinds!!! But...I am concentrating on the 'surprise' relationships that are cause for more grief than anything else. The ones you didn't see coming. Such as love scams. They are all over.
Beware of anyone who messages you and says they are in love with you after a couple of chats. They can be very convincing. Most will not do webcam. You should insist on it. However, there are some that will do webcam immediately. They are well educated, polite, sincere and very gracious. They slip into your heart before you know it. Usually very good looking. Very complimentary to you as well.
They play on your weaknesses and they are good at finding those things out. By the time they have sent a friend request, they have investigated you thoroughly. They know what you post, what you respond to on other's posts, the groups you belong to, your friends, likes and dislikes. They work these things into the conversation little by little.
They may start calling you their 'wife' or 'the one they have waited for all their lives'. But, they show little emotion. Rarely react or comment on your posts. Almost like robots. Some may try to start a sexual relationship. Eventually, their demands get more serious and they may ask for small amounts of money or ask you to join them in a business. Little things at first.
If you are discerning, you may have felt uneasy about the relationship early on. If this is the case, be very careful. Don't accuse, just slowly back out. By now, they may have your information. Report it as soon as you can when demands start. You may have difficulty with this because they were 'so nice'. You may question yourself. Once again, I have been there. I really don't make this stuff up!!