I think every good workplace tries
really hard to discourage relationships between employees, even if they can't ban them outright (because people will be people).
The basic problem is that, you go to work to work. If you go to a bar or a club or a party or a bookstore and someone there is coming on too strong, you can leave. It's nicer if the club or host or bar or bookstore makes them leave, but whatever, there are other bars, better bookstores. If you're at your job and a customer or a fellow employee is coming on too strong, and your employer doesn't do anything about it, you have the choice of "dealing with it" or "not having a job".
And people need a job; they're there so they can pay for rent and food and (if they're lucky) change the world for the better. Even if you work at an online matchmaking company, you're going to work to find dates for customers, not for yourself. Any finer discussion of the appropriate way or time or number of times to ask your coworker in accounting out is completely missing the point: your coworker in accounting shouldn't have to put up with any number of advances, no matter how mild, when they only show up at work each day to do accounting.