Fun topic!
From what I've seen there are 4 types of reactions that you typically get from marks and they can be sorted into these groups:
The Good Sport - This guy acknowledges and respects your craft. He understands the time and skill that we put into doing what we do. They will typically congratulate you on your new found treasures and perhaps politely ask for a buyback. They are not very common, and it is always nice to find one, but honestly they are kind of boring for my personal taste. I know how awesome I am, the last person I need telling me so is some silly mark.
The Rager - This guy values his stuff more than his own dignity. I have heard ragers say all kinds of crazy things. I have had them call me every name in the book, they like to make their silly empty threats and go on about how they are going to kill you every time they see you (which is extra hilarious if you are wearing a disguise kit), I have even had one page a GM on me. These guys are my absolute favorite and are the reason why I do what I do. They are much more common than "The Good Sport" but it still takes a bit to find a good one.
The Silent - Not much to say about this guy. He's either too dumb to realize what happened to him or he's raging inside and doesn't want to sacrifice his dignity by showing it. I like to assume it's the former, but I know that generally it's the latter. These guys are about equally as common as ragers and they are the most boring of them all. Usually when I encounter one I try to goad some kind of reaction out of them because, let's face it, reactions are the best part of stealing and at least to me, not getting one is unacceptable.
The Pretender - This is probably the most common type of mark. These guys like to pretend that they aren't crying on their keyboards as they tell you how worthless the item(s) you took from them are. They say things like "I hope you enjoy my garbage," or "I was about to throw that away anyway." It is because of these guys that those of us in THIEF [^_^] often say "Everything you steal becomes worthless as soon as you get away." We're not dumb, we usually have some idea of the value of items before we take them. Why else would we take them? Also, I really don't care about the item's value to the mark, after I take it, it's mine anyway. If you are this type of mark, you should know that we are making fun of you to our thief friends behind your back and we know that you are secretly crying at your desk, trying to hide it doesn't help.
I will probably come back to this thread from time to time to update it with some more specific examples but I'm at work now and don't have easy access to my screenshots.