The best weapon available in this day and age is usually the internet. Word of mouth is also a good way of digging up the truth of course, but many people tend to go on the net now.
http://www.savannah-cats.net/Not sure if you already found their website or not.. I couldn't find any complaints online.
There are many checks you should perform when buying any animal. Here are some ideas that haven't let me down in all the years I have had cats..
1. How are the conditions the cats are kept in? Is it dirty? It's usually smelly but that's just the way it is. Is it crampt? do the cats look miserable and lethargic?
2. Ask to see the mother. Always always always ask to see the mother AND the father. This is why I
would never buy a cat from a 'pet supermarket'. Here in the U.K we have a big problem with those types of places bringing over sick animals from Ireland where there are no real rules and regs on breeding.
3. Make sure your cat does not leave its mother too early. IIRC this is about 13 or 14 weeks. If a breeder is prepared to offer you the cat sooner? walk.
4. Ask to see what foods your cat is being fed. Ask what brand, what type and sort you need to feed it. Recently my uncle bought a British five point from a woman for £500. She was feeding it Tesco 'no frills' cat food.

Now I am not saying there is anything really wrong with this type of food (apart from it being shit and offering little nutrition) but if I was paying that sort of money for a cat I would want to know for sure it had been well looked after and spoiled rotten.
5. Check the eyes and the nose. If either are runny or the eyes look milky and the cat has marks on its fur from where its eyes have been running then walk. Also check in its ears. Everything the vet will do, basically.
6. Make sure your cat is as vaccinated as a cat that age can be. Demand documentation on the history of the vaccinations. Just like you want service history for a car you want the same with a cat.
7. Spend time with the cat before you bring it home. Go to the breeder as often as you like and ask to have the cat for some bonding time and also to learn the personality of the cat. Some breeders will get shitty about this, but if they do then find another one who is more friendly and open. Again, I cannot emphasise enough how imporant that is. Many breeders are ruthless and cruel and see breeding exotic cats merely as a way of making money. The good breeders show affection to their animals and it shows. When I went to collect my first girl I was shown where the mothers and babies were kept. It was immaculate, beautifully laid out and every single one of the cats in the milking cages came to greet me and talked to me.
I am sure that others can add their wisdom to this, and maybe soon we can do a sticky. I have mentioned this before but when I got my girls (both retired queens) I spent many months scouring around for as much info as I could find. I feel kind of guilty about this as I love Nicola and Douglas to bits but being an asshole pales in comparisson to falling in love with a bundle of furry joy and it dying leaving you devastated. Mind you, I suppose that just compliments Nicola and Douglas all the more, as I rejected many cats form many breeders who weren't straight up with me. I asked one guy about the mood of the cat he was offering me and in the end forced him to admit that she just hid all day, crapped on the floor, hissed if you went near her and so on.
Remember, be SUPER vigilant. It will only end in tears otherwise.