The only time I've tipped was when we were planning a one month trip to Australia and the "friend" who'd been saying for months that she would house sit bailed at the last minute. We found a woman who was recommended by our dog breeder who agreed to come for 2 weeks on short notice. I paid her almost double what she'd asked. (The other 2 weeks were covered by the son of a friend. I paid him well, too.) I figured it was cheaper than canceling our trip, and I really appreciated her being there.