Like example said, you have to be straight up with all parties. The earlier you do this the less feelings are hurt on both sides.

If it's casual let them know "I'm not looking for anything serious" or if it's just 1 night say outright "I'd love to give you my number but i think that would be a mistake" be honest and firm in a diplomatic way!

The moment it feel like they are attaching or detaching themselves just ask a straight question "where are we at?". Recently I've done this and it felt awkward to begin with but i realised it was only me making it awkward, once the girl sees that I am at ease with the question and any answer that may ensue she will feel comfortable telling me "I have feelings for you" or "I think we are a bad idea" at what point I just smile and tell them no worries.