I always turn on the charm at the airport--from the TAs to the TSA grunts to the GAs, FAs, and pilots. I figure 99% of the people out there flying are either idiots, as$hats, rude, or rude as$hats, so a little sparkle might help improve their day. (Plus, it makes me feel sexy when men respond with compliments, which ain't bad for me, either!

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If airline employees decide to treat you nicely back with a bennie of some sort, it's at their discretion.
Sincerity is a key factor. Fortunately, most people can spot a phony a mile away, so those transparently laying it on just to get something are usually too obvious. Besides, the airline employees know what's what--they wield the power. Is it any wonder they sometimes orchestrate a dance between them and us poor minions, grovelling for a possible perk, no matter how small??
Reminds me of the time I was upgraded to 1st at the gate 10 years ago on a DCA-CLE flight. I had no idea why they did so (was NOT a FF) until a pilot dead-heading to CLE sat next to me in F and started chatting me up, eventually asking me for my number. He obviously asked the GA to upgrade me so he could talk to me: I knew it, he knew it, but as I happily drank bloodies on the way to CLE, I was more than happy to dance the dance.
Flirt on, I say. At the very worst, it will give the GA something to laugh or roll his/her eyes about, and the very best, you can be flying in style. No harm, no foul.
And yes, I'd cheer on an upgrade for someone nice on a discount fare over a million-miler-butt-in-the-seat meanie with uber-status. Human decency, man. It's about decency.
big V