Regarding crayfish, I was going to do the following (if I ever do decide to use them as a staple food source for my fahaka when he's older):
Have my LFS order a whole box of feeder crayfish cheap, buy every single one.
House them in their own tank or rubbermaid stock tank with the water level lowered a lot from the top (they are great escape artists) and just feed them myself for a few weeks to make sure they are fed properly and aren't diseased.
And to be honest, not trying to argue here... (PURELY my opinion here!) But you'd risk just as much chance of disease feeding fresh market foods that haven't been frozen or cooked. (Mussells, the kind markets usually sell (the marine type I believe) they are pretty much guaranteed to actually be harvested from brackish/bay/estuary waters and marshes, so they very well could carry bacteria and protozoa that could theoretically harm a puffer)
While I agree 100% that it is healthier and cheaper in the long run if you do it properly to culture your own live foods of snails or crayfish... Puffers are specialized predatory fish used to constantly consuming live animals in the wild. So unless you feed a visibly infected live food I'm sure the puffer's immune and digestive system can handle it.
Just make sure that if you feed live foods that they come from a clean and healthy source and you should be fine. In the event that your puffer does actually become ill from introduced disease it was probably triggered by stress on the puffer from poor water quality, an injury, or another form of a lot of stress. It's not like the effect tubifex worms on African Cichlids where if they just ingest one worm that can become extremely ill and infected even if the worm itself was alive and healthy at the time of feeding (keep in mind that all puffers have already been introduced to non-sterile aquaria worldwide and have already been exposed to many bacteria and protozoa (for example, my fahaka can be traced back from my tank (which was cycled with a seeded sponge from my Malawi cichlid tank which has wildcaught Botia histrionica and F1 cichlid fry from wild parents that came from Atlantis which and then Lake Malawi holding vats and then the Lake itself), to a local importer that regularly imports from all over the world, to Aquarium Glaser in Germany which I also doubt uses any form of UV sterilization on all of their tanks, and then to african holding tanks and then african waters themself. That is a LOT of exposure to world wide bacteria and protozoa).
I am NOT trying to pick a fight here, just explaining that IN MY OPINION YVRdarb is correct in saying that you risk introducing disease (which would be minimal risk in my opinion), but for the wrong reasons as I explained above.
Personally aside from possibly buying a box full of live feeder crayfish (and quarantining and gutloading with krill, fillets, frozen market shrimp, etc) I don't really plan on feeding those myself (other than as a potential treat once in a while). I was going to just stick with fiddler crabs and snails and local blue claw crabs when the puffer is full size for live foods, and stick with (well, also live for some of these but not in the same sense as the previous ones listed) Mussells, Clams, Crabs, Escargot, etc from the market (except for mussells which are easy to harvest from any unpolluted marsh where shellfish harvesting is permitted).