[Jiocus]

I'm a paying user so I can't speak about the free Spotify experience, but..

Spotify will only repeat a song during shuffle if you also activate repeat. It will also repeat a song if you actually added the song twice or more to said playlist. You can try it out by shuffling a playlist+deactivate repeat then check which songs have been queued from start to finish.

Smart Shuffle -despite the name- is more a playlist function than a shuffle function. It's like the Radio playlists but with the songs interspersed temporarily in your own playlist. Note that these songs were not already in your playlist - so they do not repeat unless you activate repeat.