First, let me give you my condolences on your tragic loss, my heart aches for you.
Second, having asked the questions you felt were important to know the extent of this person's knowledge of sugar gliders and that she (and for no reason you would know otherwise)was able to convince you that she was a suitable care taker for your suggie babies, you did for the most part all you could do to ensure that, and what most other people would do. (I use "most" only because there may be some that think of things most or average amount of people wouldn't think of).
I have three suggies that were all re-homes, here is brief description of the process I obtained them.
First, a pair of females, approximately around a year old, being 2 months apart in age and from same breeder. I found them on CL, they were fairly local, about 30 or so minutes drive from me. I emailed seller, I received a response answering the questions I asked (I was limited on my questions because I wasn't educated properly, being I was going by what an acquaintance was telling me) and given phone contact info and address. I was invited to come see them before making a decision. At no time, did the seller ask to see my home. She explained the care information she was given from the breeder and the diet and how she fed them, she showed me their cage and let me see and try to pet them. One of the girls, Lulu was not friendly, the other Skadoosh was pretty friendly. I left and considered whether to go ahead and get them. I decided to do so.
My third glider, a single male, neutered and around four years old. His current mom at the time had him with an older female and when the female cage mate died, she had him checked by vet. He was found healthy, but with her school schedule and finances she really couldn't search for a new mate for him and follow the protocol necessary for introductions and so decided to remhome him. I saw the ad for him on another forum I frequently visit and since he was alone and not too far from me, I contacted her. She had seen my posts on the forum and after talking to me more in depth felt comfortable re-homing him with me. I had offered if she wanted to visit my home first to see the arrangement ahead of time, and she said it wasn't necessary. She brought him and his things to my house and helped get him set up where I had to keep him for quarantine and although sad to leave him behind, I believe she was confident he was in good home and would soon have friends.
Anyway, I know I said brief, lol. I wanted to point out that at both times I homed gliders, neither former keeper of these precious animals saw the home prior to, that they were going to. They trusted me, merely through their impression after talking to me. As it is, I was honest about any intentions and always had the gliders best interest, as they believed.
My point is, not asking to see their new home does not make it your fault she was not what she presented herself to be.
In addition to that, all the pets I've had, whether adopted through spca or rescue or from a breeder, and purchased from pet stores, no one has asked to see the home in which these animals were going to.
Please know, that even if you had gone to her home, you may not have known what she really was if she could have staged anything prior to your visit.
I am so sorry that you had to go through this, and feel the way you did, ashamed and blaming yourself for so long that you didn't have the support from friends and fellow glider loving members to help console you.