I talked to a management agency recently and they advised me not to put a washing machine or dryer in a rental house. He said the problems would be huge with tenants clogging up the machine, etc., and he had various horror stories. He said, "Tenants won't expect one." I was surprised, but he was very persuasive.
If you do get a machine, one way to avoid their friends doing laundry there would be to make the tenant responsible for the utility bills.