OK Firstly the stock house can really only be used to show anyone who may be interested in buying it or another of the same housetype is no show home exists. It is usual and a good idea to run the heating but that's as far as it goes.
As for the washing machine, they don't need running a cycle every now and then. Otherwise Currys would have lots of washing machine working in their stores!
The cat is a non starter as how did it get in? Do they leave the doors and windows open during the day?
Why did they allow a cat to get in?
My guess, is that the sales advisor has been having sex in the house and was doing the laundry!
Why else so many excuses and explanations as to why the washing machine was on.
If he/she had a brain they could have said they were just washing a few tea towels for the sales office which is believable but taking them home would still be easier!
What you are buying is a nee house, with a second hand washing machine.
If your solicitor wasn't recommended or suggested by the housebuilder please speak to him.
If you are having second thoughts you can cancel now no harm done. After Exchange you are trapped and have less power.
Buying a showhouse