I am not buying a glider, or any other pet, from a petstore. Breeders only for me, from now on. I visited another petstore that advertised, via a sign on a wall, that they had a "very tame 6 mo. old female. Cage, glider, and all accessories for only $100.00." I inquired of her whereabouts to find that she was directly in front of me! She was brought in by an owner no longer wishing to care for her lonely, very crabby self in the smallest bird cage that I have ever seen...it was only 14" high and square. I asked the clerk what they feed her (though I am not a glider expert, I do know what is wrong). She said "various pellets from the other pets within the store and hotdogs". (she honestly said this!) I asked if the glider ever receives mealworms, etc., she said, "Oh, no. They should never eat insects."
I noticed early from looking around this petstore that they were also selling 3 Degus; mom and her 2 daughters. I own 3 degus myself (I have more knowledge/experience in these critters so I asked the clerk another question) What does she feed the degus?
"Only Rabbit pellets and lots of fresh fruits. *OMG* (...this diet will make degus diabetic!)
I left soon thereafter with a terrible feeling in my gut that I should have 'rescued' the glider and 3 degus.
But, like you said, more critters will take their places if I purchase them. It is so horrible that critters must suffer at the hands of the ignorant, or those who could care less. I so wish that I could become a 'rescue or foster haven' for critters so they may in turn discover the love that God intended for them.