You have to figure that a lot of antique dealers buy entire estates, complete households of stuff, from soup (I hope not really) to nuts, and there is no way anyone can know about every field --- when you're knowledgeable about particular areas you're bound to run across dealers who aren't specialists in your area, and may be selling for a bargain price something that you know is worth a mint (or at least significantly more than what they're asking.)
It's not all that different from my usual thrift hunt -- just maybe less "oh, wow!" and more "they want HOW MUCH?" The plus is more concentrated content
- you don't usually have to slog through stacks of cheap junk to find a few goodies.
I also look at antique malls as a sort of grad school - best way to learn about things like that is to look at them, handle them, note the details (literally - I carry a pocket-sized digital recorder and make notes so I can do research later, to understand what I have seen), and ask questions if you can!
As far as what I've purchased - everything from a cast iron floor grate for my 1920s house, to a bed, to an old carved wooden mortar and pestle set (I actually think there's another name for what it is - much bigger than what you think of as a M&P - but I've never really looked into it. I just liked the workmanship SOOOO much, and the price was right.)
