They identified and used your insecurities to make you like them more. If you were shy, you suddenly felt like you became the most interesting person in the room. If you were overweight, you were suddenly the most gorgeous person they had ever met. You felt special when you were with them.

They gained your trust early. They shared detailed personal stories about their life early on. The purpose was to get you to share information about yourself.

They were impressive. They told you stories of impressive performance in business and incredible success in general. Their air of confidence convinced you the stories must be true, even though you didn't see anything to verify this. Sure, they drove a crappy car but that is because they really loved that model, not because they didn't have the money to buy a new one.

They manipulated your sympathy. At the start, they had a story about a hard childhood, a bunny-boiling ex, a recovery from cancer, or something else designed to elicit sympathy in you. It was probably short on verifiable detail and unlikely to be true. The purpose was to gain your pity and attachment. We are much less judgmental about people we feel sorry for and much more likely to reveal our vulnerabilities to them.

They surround themselves with fans. Once you are hooked, they will start keeping company with other people – new potential partners. This is to remind you that you are lucky to have them and that they have plenty of other options. As a result, you feel constant anxiety about your relationship.

They have no past. You will rarely be introduced to anyone who knows them from before you met. These people will not give good reviews, so you are kept away from them.

They will sabotage and sever your relationships. They will work hard to cut you off from your friends and family. They will work to make you feel uncomfortable around the people you used to feel most comfortable with. They want you to be dependent and loyal only to them. They do not want other people telling you your partner is a nutbag. They are jealous and they will actively exclude potential partners from your life.

They lie constantly. Often when there is no reason to lie at all. But they always have a plausible explanation at the ready.

Nothing is ever their fault. They are fantastic at rationalising their behaviour but never change it.

They deny their own previous statements and behaviour. They dismiss your attempts to present evidence of lies and, as a result, you often leave a conversation with them doubting your sanity. You will frequently be accused of being too sensitive.

They are parasitic. You pay for almost everything. They will move into your home. They will use your car. They will often need to borrow money from you.

You become yesterday's news. Once they have hooked you, you seem to suddenly bore them. They give you the silent treatment and rebuff you for trying to rekindle the relationship you thought you had. They will sometimes disappear for days at a time with no contact and no explanation. They are usually working on the next conquest during this time, or are simply two- (or three-) timing you. If they sense this pushes you too far, you will get a little more love-bombing to reel you back in.

You will be dropped like a hot potato. When they have decided you are no longer of value to them, the relationship will be terminated like it never existed. You will feel isolated, insecure, insane, shocked and empty.

Edited extract from Taming Toxic People by David Gillespie (Pan Macmillan), published on Tuesday