Roundup. We always sell bed-weeding as a part of our contract. You can add a lot of value to your service if you also maintain their beds, and with round-up it is so easy to do. If you really want to do it quick, cut it down the ground like everyone was saying, blow it into the grass, mow over the clippings, and then spray roundup. From the sounds of it, they probably don't like being able to SEE the tall weeds. If they are on a tight budget, I highly doubt they will complain if the weeds are cut off directly at the ground and dead. But the longer you go back and forth with them, the pickier they will be when you actually do it. Take care of it with round-up immediately.