This is an easy one, but hard to explain
If it is a person I like to have in my company, I don't mind too much being persuaded, as long as it all stays in a friendly mood and is more teasing around. There is no harm in letting a girl know you're into her. It's complimentory and as long as you stay nice, respectfull and airy about it, without pressuring, who knows maybe a girl will change her mind someday?
But if it's a clear no, where it is unmistakable not appreciated that you ever repeat that behaviour again, it is very respectfull to back down. You can still be friendly around eachother, but don't flirt under any circumstance.
Still don't know if I explained it right, though.
If you get the feeling that the "no" could just as well be replaced be a "never in my life", then back down. In any other case, feel free to try again untill you hear the previous "no"
Wasn't aware, meant for the best, ignorance is no excuse, but neither is insolence - a polite pm would have sufficed