My definition of a blurb is that it's like a taster for the pie - a small sample to tempt the buyer. It isn't a synopsis.
A synopsis is what you would send a publisher, this details all the major/minor events in the story and the relationships between the characters. This is done to give the publisher enough information to know a market to pitch the story.
The two-minute window
This is how long you have to catch a buyer.
You need a good cover, eye-candy is vital for the first step for a sale.
Stage 2 is a catchy title - not more than five or six words.
Finally, a good blurb to link the title to the cover.
I used to be good at writing blurbs, two of my best blurbs enabled the writers to gain contracts in magazines - but I never even got a thank you note from either of the writers.