Been there, done that, got the T shirt to prove it. It happens all the time to both widows and widowers. I have several close friends that have been widowed and many of the middle aged ones with a decent amount of financial resources have been targeted by the not so well off. Golddigging is alive and well.
Having some one throwing themselves at you when you are still mourning sucks.
You learn to be careful about people. I got lucky and found a really good woman and my experiences with "other types" was thankfully limited but educational.