To date or not to date?

So a friend of mine recently shared this dilemma with me and asked for advice. Just thought I'd put it out there to see what other people think about this situation.

So you meet a guy or a gal and you guys have instant chemistry. You like each other.....You like the persons looks, personality, sense of humor and you have similar goals in life with the person. You think that this person might just be the one for you and you wanna pursue things to maybe have a relationship with this person. However, before things get too serious you find out that your potential perfect match is married. Where do you go from there? Do you take what the person tells you about their marriage into account or it is game over right there?

Would you or would you not get into a relationship with a married person regardless of the circumstances or would you date a married person depending on what their specific situation was?