Is there anything one can do to train seniors in how to deal with these agressive con men?

Your mom sounds amazing for her age, but she's no match for this kind of scam. You are right that she could be physically harmed, as well. I'm not sure where you live, but maybe there's a neighbor who could watch out for her. If not, she may be better off in a community living facility. She won't like the move, but 89 and alone is tough.
Unless, of course, there's a college student or someone you trust who could live with her? That might work, but you need to be very sure you can trust that person, of course, or you would be going backward rather than forward.
I'm glad the police were informed. This situation is appalling.
Take care,
Carol

Thanks Carol,
There is a neighbor across the street that does keep an eye on the neighborhood, but for some reason my mother has had a falling out with him. Do you think reporting something like this to the local newspaper helps? The neighborhood she lives in used to be a much more closely knit community, but so many of the older, familiar have passed on. The newer, younger neighbors, more or less keep to themselves. She is very resistant to moving, she wants to stay in her home as long as she can. How would one go about finding a college student to live with her?

Never answer the door! Really there is no reason should a person have to answer their door when you think about it. The people that should be coming over can call first to let your mother know they are on their way. You can place a key in a place outside that no one would think to look and let those people know. Make sure that key is put back in its place once that person leaves. That way the cons cannot have access to get in the house without breaking in. Should they power wash the house again without her permission, they are sunk. They will not know if she is home or not if she does not answer the door. And keep her away from the windows! We have sheers in mother's house. With heavy drapes over them. I can pull the drapes back a bit and let sunlight in but no one can actually see in. Her lights are on timers. Also, I got mom hooked on a door jam bar. It is a bar that is put under the door knob that reaches down to the floor. (they are adjustable) This bar keeps people from strong-arming their way in entry ways. I have one on my front door, back door, kitchen door and even my bedroom when my husband is away. They are very inexpensive and check with Lowes, Home Depot, Walmart, etc because each one can handle various pounds being forced on them. (Say like a 300lb man trying to strong-arm his way into the house by kicking it or putting his shoulder into it.)