exactly the same experience , offers going down and down, and then , if we can use your windows as a local reference site - then even cheaper again , this was in late 1990's early 2000's , cant remember the details but it started 4/5 times the final price - I also asked them to leave ( 2 bods) and had a bit of an argument to actually get them out of the house.....to the point, where i was almost at the point of getting my partner to call the police - she had already left the room.
My neighbour in her 80's had the same issue with a kitchen fitting organisation, can't remember the name exactly, but i met them and also had trading standards on their way , they were very interested and sent a guy round to also meet these guys, they didn't turn up.