You just have to give it a try.
If they're a player who tries to do their best and you say "oh btw (name), interested in a few tips for SMN?", they'll be happy to know and it'll lead to a learning experience for them. If they ignore you or politely decline, not much you can do but at least you asked. If they're playing extremely bad, are very undergeared, get rude, aggressive or tell you to shut up because they know everything and play Ultimate on that class (lie), kick them.
But it's always worth a shot. You have nothing lose (the above inquiry is worded too nicely to be seen as abuse) and potentially help make a better player.