Negotiating with Caterers

I must admit, I am learning as we go. I have no clue how much I can negotiate with caterers. I basically took their price and then filtered from that point on. If they were too much, then I moved to the next person. Well in comes a caterer that we put a deposit down to save the date. He gave us a fairly large bid and I basically discarded him, but he was persistent and agressive. So we switched from full sit down to a buffet in order for him to come more in line. Well the future Mrs went to an event for which he was catering for and he asked "What will it take for you to hire us?", so the Mrs' responded "I really want sit down and another hors d'oeuvre." And I put the rest down:
Caterer "How about if drop 1k off?"
Mrs "No"
Caterer "2K"
Mrs "No"
Caterer "3k"
Mrs "No"
Caterer "Ok, how about XXXX out the door"
Mrs "Ok"
Caterer "Ok I will draw it up"

So essentially the guy went down double digit percentage points in a matter of minutes. The question how much are these people really making.

So now I got one bid in that isn't your normal wedding food, but a little something more, but I haven't even tasted his food. So to not put all my eggs in one basket, I started emailing more caterers. They send me menus, prices, etc... and I just give them a quick glance, but don't really care about formulating a menu. Then I reply, I want this that this and that and want it for this price (of course less than the other guy) and wait for a response. They either say this is the best we can offer or actually beat it. Man now that I have a baseline, I can skip all the BS and get to the beef.