Buskers: The simple rule is it is never live. Sometimes the amp is in the instrument, but when you see a big amp know the following
You can buy instrumental tracks from places like Sound and Vision, South Street, Elgin in MIDI format. I.e. all of ABBA’s songs for a few quid. With midi software such as steinbergs cubasis it takes under a minute to change the lead instrument to your own instrument. You just reasign the instrument to the track. You can also mute unwanted instruments. I. e. the pipes and drums of the entire british army. Or all the fiddlers rallying somewhere. (They don’t play anything either)
I believe they use tiny USB pens now.