What: Shares of Sotheby's (NYSE:BID) dropped 18.3% in the month of November, according to Capital IQ data, after reporting a quarterly loss.

So what: Third-quarter revenue jumped  46% to $138.0 million but net loss for the quarter was still $17.9 million, or $0.26 per share. This is traditionally a very weak quarter, so a loss isn't surprising but the warning signs being given by management haven't given investors much confidence. CEO Tad Smith said on a conference call after reporting earnings that high-end buyers are becoming more "discerning" and that could mean that the waning stock market could take its toll on Sotheb'ys.  

Now what: The last six or seven years have seen a boom in income for the richest people in the world, but that's been driven in part by low interest rates and rising stock values. But interest rates will soon begin going up and the stock market is hovering right around breakeven for the year. Sotheby's management is warning that these market conditions could lead to tougher times ahead and that's what investors were focused on in November.