Mysterious, REPEATED Finch Deaths

Question
I'm trying to get my wife a female wax-bill finch to match her male, so she'll have a breeding pair.  (This is supposed to be a Christmas surprise).   I'm more of a cat/dog person, so I'm guessing about exactly how to care for them.

In summary, I have bought three female finches over the last week, and all three have died.  I'll give the details, as that will hopefully reveal something to the experts.

#1: Purchased at local PetsMart chain.  I also bought a medium sized simple cage.   I took the finch back to my office, about a ten minute ride, in the cardboard container and released into the cage.  I added paper towels as a cage liner, water, and oops, forgot to get finch food, so I added a little tray with sliced apples and trail mix, and replaced it with finch food the next day ("Wild Finch Food" from the grocery store.). The little finch didn't seem very energetic or cheerful, but, I'm not a bird person, I figure it's just the transitional stock.  I come back into my office the next morning and find it dead on the floor of the cage.  (My office is an old house that we run a consulting company out of.   We clean it ourselves, so there's nothing weird that happened out of hours.  It's all paper/computer stuff; we don't use anything more toxic or industrial than, oh, a laser printer or a coffee pt.)

#2: Back to Petsmart.  They apologize, replace the bird with another one.  Both I and the bird-guy there think it looks a littled "fluffed up", but what the heck.  I go back to my office, carefully wash & sterilize the cage with a mild bleach solution, dry it, and put the new finch in.  I give it fresh water and a new finch food which is the same stuff the Petsmart uses.  Happy cheerful little finch.  Dead the next morning.

#3.  I go back to the Petsmart.  Get another one.  Take it back to my office, sterilize and clean the cage, put it in there, take it to a neighbor's house, leave the happy finch there, with the new food, fresh water drawn from their taps.  I get a call this morning: this one is dead too.

I am dreadfully dissappointed and puzzled here.  The only variables in common here are me, the Petsmart, and the cage.  The three did not stay in the same place, eat the same food, or drink the same water.  Could there be something going around amongst the finches in that Petsmart that the transition shock brings out?   The bird-person there seemed conscientious.  I purchased a Carbon Monoxide detector on the way back to my office after #2 and installed it; it did not register any CO or natural gas there.  I made an effort to not expose #3 to my office, in
case it was something poisonous there -- I kept it in the cardboard box until I'd cleaned and dried the cage, then moved it there, using the breezy foyeur of the building.  

Clues?


Answer
Alright, well, first mistake; getting the birds from PetsMart. I find petsmart has no idea how to care for birds so most of them are sick and ready to die at the store. Go find a breeder, they usually have healthy birds and will show you what they feed them and where to get it from.
Second mistake; using "Wild Finch Food". When it comes to birds, you can't cut corners. Dogs/Cats can handle it but birds can't. They die very quickly. Getting nutrient fortified food from petsmart (and PJ's) is the best/only way to go.
Third mistake; you didn't take a good look at the birds there. You're new at this so I won't give you a hard time. Pet store birds often have something called "Air Sac Mites" this is where little parasites go into the throat and lungs of the bird and stay there living off the blood of it's victim. Eventually there are so many that the bird can't breathe and suffocates. Easy to tell if a bird has this. Hold the bird up to your and listen for clicking. If the bird clicks while it breathes, it is infected with these little buggers. It's treated easily enough with something called "Scatt". This can be purchased online at www.ladygouldianfinch.com or www.ladygouldian.com. The owner of the second site is very knowledgeable about finches and will be able to help you learn how to care for your feathered friends.
NEVER USE IVAMECH ON FINCHES! This is something the petstores use when their birds are infected with the mites. This treatment has killed it's fair share of birds. It's too strong and it's easy to OD a small finch. This stuff is almost too powerful for the larger parrots. Stick with Scatt.
You should also be watching the birds before you buy them. A healthy bird will be hopping/flying around with well groomed feathers. A sick bird will sit in one place with it's feathers puffed and look very sleepy. A bird on the bottom of the cage looking like this should be left alone don't buy it. Also, when in doubt, buy a book. Many petstores offer "how to" books that tell you how to care for finches. All you have to do is find one that has a lot of info in it and follow it to the letter.
If the next one one dies, freeze it's body until you can get it to an avian vet. Have them do an autopsy on the thing to find out the reason for death