Yeah, but in my opinion, the store will do whatever it takes to wash their hands of ANYTHING to do with this if at all possible once they learn of this. And once you start asking any questions, that will INSTANTLY sound the alarm to cover up any possibilities of it originating from their store whatsoever!. As soon as he left, more than likely they would be getting rid of every single rodent there was in the store..LOL!
To me, it is better to go in there AFTER it is known that it was indeed the store's rodents and saying..."okay folks, see this toxicology report??, this is what my veterinarian found caused my snakes deaths shortly after I purchased some feeder rodents from this store. Now do you want to do this the "easy way"?, or the HARD WAY??, the choice is yours. You can pay me a very fair price for replacing my snakes that died, or we can go to court and you will STILL pay me for my snakes that died, AND any and all other additional expenses that will be involved. It would be nice if we didn't have to go that route, don't you agree?
Also, like Jeff said, you go in there and get some more rodents BEFORE any of this is brought up so they can be tested if need be BEFORE the store is alerted to get rid of all the feeder rodents so there is nothing to go on!..LOL!. The last thing the store will want is for the path to lead directly to their feeder rodents.
Making sure all his "ducks" are in a row is key to any closure here. It is doubtful that anyone working there is going to divulge any info on where they get their feeder's from just out of the blue voluntarily once they sense a big problem is on the horizon, and only the upper manager personel would probably know anyway, certainly not the kid at the cash register, or the other kid in the small critter department that grabs them by the tail and drops them in the paper bag and staples it shut...LOL!
See, asking them anything will only let them know there was a serious problem. He wants the ball in HIS court, not theirs!. That's why he will want to march in there AFTER he buys some more rodents(and keeps them in case they need to be tested), and AFTER he gets some necropsy results that can hopefully conclude it was the stores feeder rodents.
Now if the necropsy results come back inconclusive, then he would have no proof of anything bad causing the snake's deaths from their store, so he THEN he would have nothing to loose by asking questions since knowing the cause from the vet is out the question.
The timing of the well-planned sequence of things here is key. Not walking in there asking questions so the owner can get rid of everything and get the employees together to get a good made-up story concocted. 
~Doug
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"a snake in the grass is a GOOD thing" 
my website -serpentinespecialties.webs.com