Selling to a Developer

[Seattle Matt]

Hello, I'm relatively new to the forum, but I've been lurking for a few years.

I'm just about to list my home in Seattle for sale, likely with Redfin.  Since they have rezoned my neighborhood I have received inquiries from developers. 

I developer offered me 675K with an optional 12M closing.  My potential agent would like to list around 700K, I am thinking 725K.  Zillow has the value at 697K.   

What are some of the drawbacks to selling directly to the developer?  What if they back out and the market goes down?  Hidden costs, etc?