It is not just Facebook, there are a TON of fake web sites out there, If I have no experience the first thing I do is simply search ( is "the web site" legit) there are several scam detectors that will pop up and rate the sites and there are allot that fail the scam detector, if they pass and it is going to be a major purchase I will ask on a related forum if anyone has done business with them.
Lately I have been buying allot of reloading supplies and have found many scam sites, most look really good, evidently it is rather easy to whip up a legitimate looking site.
All the scam sites I have found respond almost immediately that they have the item in stock and to go ahead and put in my order, probably an automated response.