I have done this as a favour to various neighbours, yet feel rather taken advantage. No payment is requested or given, but I have been surprised at the lack of gratitude. I have been told it is only a cat, only to find a menagerie of animals with complicated and time consuming instructions. When I arrived to collect keys I was told the timing wasn't convenient and to come back. When they return back: nothing, not even a thank you card. I have had this before with another neighbour, who after visiting their cat 3 times a day for a week, couldn't even be bothered to collect their keys.
I have also been faced with filthy houses. I don't expect them to be spotless, but I am surprised people would leave dirty dishes out and food splashed on the wall, maggots in food bowls, when they know they have someone coming over to feed pets.
For context, they have never returned the favour. If they had engaged a service to feed the pets, the cost would have been at least £10 per visit.