At some point, your renters will likely pay a bill for you. Perhaps they’ve been nice and done a repair themselves, and of course want to be reimbursed. The concern is the much more likely scenario: they have had to pay a bill when a repair was done, and you weren’t able to set up payment otherwise. Not only will you want to reimburse them quickly (that is the professional thing to do), but you also want to be sure that you’re paying them the correct amount!
So what is a nice, easy way to ask for proof of the amount owed, without implying that you don’t trust them? Blame the government! You only need to say “Please send me the bill, so that I have a record for my taxes.” Not only is it true, it’s also universally understandable. No one will ever be insulted or hesitant to provide the information.
This is useful information, even if you have a property manager.