Alright now you know it's BACFM to answer your questions
1. Should i bring my cooler for frags?
If you plan on buying frags abso-freaking-lutely! However I wouldn't bring frags unless you have trades pre-setup, or you have something really out of the ordinary that people would absolutely gobble up and want to trade for.
2.Is it a real "swap" or more of a go and buy type of thing?
It's a go and buy type thing, however the way they set it up is that these are "higher end" corals, you're not likely to find "common" stuff, and it can be considered really pricey, especially to those who don't know any better. No swap though, however they do have raffles & auctions.
3.Can you "debate" a price for a frag??
I don't see why not, the worst they should say (if they're professional) is no... unless you're really trying to undercut them. If you want seriously good deals, stay there until the end, and many will give deals somewhere upwards of half off, simply so they don't have to pack it up and take it back. If you live in the area it's great because you can go early to pick up something you absolutely MUST have, then come back later for some deals, otherwise you should come either early or late depending upon if you MUST have something or you want some good deals if you're not going to stay all the time.
4.Are they usually real expensive rare stuff or what?
Usually "less common" stuff, however not everything is "real expensive" yes you'll find frags going for $100+, but there are some that sell $10 frags, some $20 frags, etc. Don't go looking for a colony of something or other though, one I went to, one guy sold stuff for $5 a frag at the end, and I got a couple nice pieces, but it wasn't exactly higher end corals.