How can you tell if a guy's flirting with you?

so I guess I'm bad at telling when a guy is flirting with me. my friends always claim a guy was flirting with me and I always say he was just being nice but they insist it's flirting.

here are my last two recent examples.

we were at a sandwich shop and I asked for honey mustard. the guy said they didn't have any and I said they had it last time I was there, and he said they didn't have it any more. then he said he wasn't supposed to tell me this, but if I called his boss and complained they'd probably start offering it again.

flirting or not? I didn't think so but my friends swore he was looking at me and smiling in some special way or something.

when we were shopping at the mall and checking out the guy cashier looked at me and said "if you can name this song and band I'll love you forever". it was an obscure song but from a band I listen to, so I told him and he yelled "awesome!" and gave me a high five.

flirting or just being friendly?
How can you tell if a guy's flirting with you?
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