I'm going to chime in too, but I'm not a straight girl.
If you're working, don't hit on your coworkers. Ever. Don't shit where you eat, don't fuck around like that in the workplace. I'm not going to say any more, this is basic stuff whoever raised you should have said, it's good sense, and it's a hard rule.
If you're a customer, you've got them backed into a corner, and they know next to nothing about you, apart from the fact that you'd hit on a captive audience while they're trying to earn their keep, which is often not a panty dropper. I just picked up a stalker because I gave out my phone number to a customer, and I am never doing that again. I thought she was cute, I didn't need a million calls from private numbers, her sister on the line, and to hear her plans for children etc. I'm sure that women are far more likely to have copped this one.
More often, it's just creepy, or threatening. My friend had a customer who answered the door in his dressing gown and a leather belt he snapped back and forth between his hands. The customer had specifically requested him. Obviously an extreme example, but he carried a weapon in his car afterwards and never felt quite as safe again.
Flirting is meant to be light, fun, and playful. If you really think your flirting is that good, exchange numbers quick and do it somewhere better, because keeping someone from their job, harassing them when they don't have many options to leave, or not taking a hint, isn't sexy.