You're right that it's better to pay a tip with cash. The part that's iffy is what happens afterward. If it's as simple as handing a bill to someone who has he

You're right that it's better to pay a tip with cash. The part that's iffy is what happens afterward. If it's as simple as handing a bill to someone who has helped you out, great, that's the ideal. But if that person is required to pool that money (for example - a restaurant might require servers to pool tips, cash or credit, so that busboys and the kitchen get a cut) there's probably no avoiding the shenanigans the restaurant's management might engage in.