Not every sleeper is a good buy...

Perhaps not really a sleeper, but usually if someone pays three times the estimate, it is because they see something in the work the auctioneer has missed.

In January 2013 at Christie's, a "Studio of Rubens" was estimated at $50,000, but sold for $170,500 instead.

Now, the same work is for sale at Dorotheum (in Austria) on 20 October 2015, as "Attributed to Rubens", but with an estimate of 60,000 to 80,000 Euro, or about the same as the previous one. It has been cleaned in the two years since, revealing a lot of extra details (the complete background has changed), but nothing that improved the attribution or value. Ouch...