How can a woman know whether or not men view her as 'hookup material' or 'relationship material' and What makes the guy decide whether or not a woman is one or the other?

It's all a respect thing. There are ways to flirt and attract without coming off as easy. First of all, be yourself and have your opinions. If you are the type to agree with someone strictly to fabricate a common bond they will see through it soon enough and you will be perceived as a person who tries too hard, doesn't know themself or is generally untrustworthy. Some times, however, a man is looking specifically for a "hook up" and will play the agreeable game with women. If you can spot this, you can avoid it. Usually if someone agrees with every little thing you say they are trying to gain a certain level of trust (without actually earning it), and have an ulterior motive. At the same time, being "relationship material" does not mean going around telling men about your desire for marriage and babies, as this is a lot to take at first. Being independent, confident and self reliant are the best ways of showing your potential. A woman who doesn't need a man to succeed is often the most sought-after, they are seen as having less "baggage". That and the fact that you have your own life shows a man that you will not overtake his if in a relationship. Spending time apart and having outside hobbies and interests is just as important as maintaining a romantic relationship. I hope that any of this made sense, and somewhat answered your question!