I'm glad I came across this discussion. This is a huge issue with me actually. For various reasons I ended up living with a man that made me do all kinds of things I didn't want to do. It was awful. He kept telling me that he was just pushing my limits because he wanted me to see that I could deal with it if I had to. Granted, some of those very things I do enjoy now, but I never enjoyed them with him because he had absolutely no respect for me and my limits at the time. I left town while he was at work one day and never looked back.

Respect is VERY IMPORTANT! If someone says they don't want to do something, LISTEN! Sure, limits can change over time, that's natural. Maybe you could just discuss them every once in awhile to see what has changed. And, yes, if you know your sub very well you could softly test those limits to see the reaction I suppose. Just remember that those things are limits for a reason and some things just will never become ok.