How to tell if an artist is using a backing track at a concert

The most obvious thing is to pay attention to whether the voice changes volume or disappears when the artist moves away from the microphone, or if it stays perfect while they're on the floor in the crowd. Also watch their lips: if their mouth doesn't match exactly what you're hearing, especially in fast parts or ones with lots of consonants, that's a pretty clear sign. Another typical thing is that the voice sounds too perfect, without the small natural changes anyone has when singing live, though this is harder to notice if you don't have a good ear.

There are technical signs that help too: if you see them keep singing even though they've moved away from the microphone or they're in a spot where technically it shouldn't pick up well, or if the energy on stage goes up while the vocal quality stays exactly the same, there's probably backing track happening. There's also the fact that some concerts have a backing track that's practically indistinguishable from what the person is singing, so it's not always the artist's fault: sometimes it's a production choice.

If you want to be sure, watch videos of the same song at different concerts or in acoustic sessions: there's going to be natural variation in the voice, small mistakes, breathing changes. When everything is identical to the studio recording, that's pretty suspicious. That said, lots of artists use partial backing tracks to boost certain moments of the show while still singing live, so it's not necessarily something negative.