Ditto on the comments about the fake estate sales. I can't stand them either.
As for Estate sales run by professional companies --- they are their own animal. But - a lot of them are gold mines. I've found the best way to approach them is to get to know the people who run them and what they are familiar with. 99% of the time, you can figure out that the company is weak on something - be it glass, jewelry, period pieces etc. A lot of these people are not general antique dealers --- they are what I call "mark lookers". If there is no mark, name signature etc that they can easily google -- they miss. Remember, unless they have years and years of experience, they will not be able to efficiently process an entire estate and so they turn to short cuts. Some tips for the pro sales:
Lenses -- a lot of times they just price the camera and miss that the value is in the lenses, filters accessories
Unmarked precious metal -- its mind blowing how much of this we come across
Items related to a hot era that are not signed (turtle has a great thread on this already) - a great danish modern sculpture is a great danish modern sculpture regardless of who made it.
Stainless Flatware -- this still has not made it onto the pro radar despite my blabbering about it for a year
Books
Finally - be a specialist in at least one area. I have personally purchased thousands upon thousands of dollars of sterling jewelry and flatware at about scrap from professional dealers. E.g. - a stupid Silpada necklace -- not even vintage --- will bring 10x scrap. But you have to know what the mark looks like (circle in a double chevron - google it for examples). There is no name usually - just the mark -- too much effort for the average estate person to investigate.