Percentages really help in this particular case.
If someone is in a customer service role and are acting like they're into you, there's a 97% chance that they aren't.
Best way to see if you're in the 3% is to ask them. When you see the instantaneous drop of the façade, and the onset of a creeping, rising, chin-to-forehead expression of sheer disgust, quickly replaced by awkward mouth and sad eyes, you'll know you done fucked up.
Normally I'm all about boldness, but it might be a good rule of bum to keep your mind out of the gutter when dealing with customer service people. Besides the very good chance that you'll end up feeling like a twat, customer service people have had to develop a particular set of skills to handle their jobs. Those skills veer fairly close to corruption of the soul and evil incarnate. You don't need that. You might get banged, but you also might have to lie in bed hearing about a customer service day in hell.
Short Answer: People are awful the way that water is awful. In small doses, good. Too much and you drown and die.