It's not easy to seduce random women. Much, much easier to seduce men online, literally just need to show a leg.

These are the things that come to my mind

1) rather than a technique, they focus on targeting lonely, desperate women. Unattractive single mothers who are in their 30s or older. However if the scam involves getting money rather than an actual marriage for citizenship, then they can't target someone who is too down in life with no money, so this point is not full in action

2) Lovebombing. However this can happen only after the woman is already interested and chatting a lot romantically with the person, and afaik the scammers don't use fake pictures of unbelievably hollywood-level beautiful men for their profiles, so I don't know how they can get consistent romantic
interest online while not running an operation that is so sophisticated that they study a person in detail to create a fake man persona and seduction texts to fit her profiled needs

3) Numbers. They may be contacting a huge number of women all day for months before finding one that falls for it? Or maybe they have some way of online groups of women who are more easy to fall for this scam by what facebook groups they join or something? I don't know.

What else?