My husband is a landscape designer and some people tip some not all. It's always appreciated when people give snacks and drinks. I had a job once, it was 118 degrees here and the boys ran out of water, so my husband asked the owner of the house instead of taking the time to go and buy more, the owner of the house came out and handed them each bottle and told them that my husband should provide them with water. My husband still had to go buy a cover because 1 bottle doesn't go very far when you're working and that kind of temperature.
They are always thankful for anything they receive if the landlord isn't doing the physical work. I think a good review is enough for him.