Obviously, I immediately suspected scam, and when I called, I was greeted by a guy claiming to be from the "Federal Investigation Department."

Rarely, most FSBO I encounter are over-priced and sellers don't want to negotiate.

Truth: Only inaccuracies can be removed so these are scams too.

I understand that argument to a point, but I'd note that:1) When you quote for the job, you should do everything you can to anticipate what issues you might encounter.

Homebuyers across the country are being targeted in custom-tailored email scams aimed at stealing down payments.

Some are honestly a scam, but you can probably tell those right away if they try to "sell" you stuff. 

The basement had been clean and dry, but apparently encountered a moisture problem over the summer and now the back sides (all exposed particle board) of the cabinets are covered in green and white mold.

If so it's absolutely, definitely, guaranteed a scam.

It was Zillow and the whole time I felt I might be getting scammed.

The thing is, it's very difficult to go after people that are professional scam artists.