your customer is broke, skint, no money, hence the reason the house is for sale, I would continue to clean as long as they pay for no increase, but if for any reason I didn't like the job or customer I would dump, every customer is different and I would decide depending on them
I had one cancel last week for the same reason, selling house and lack of money, they asked if I could do it when I am in the area if they asked when they see me do the neighbours and if they have money, I said yes as they had always been good and obviously have money problems and a young family to feed, I do have a bit of compassion in me
I look at each case on its merits