I actually rather liked the Bayer Bee Guy who talked to us. He has a company story he has to tell, of course, and I take all that with a grain of salt. However, it was quite evident that he knew his stuff. I have zero doubt that he is exceptionally good at spotting reasons bees die that have nothing to do with Bayer products. He has kept bees since the 70's, I think.
What I particularly liked is his willingness to discuss their methodology that could be useful to ordinary beekeepers. I was already planning to instrument our hives, including electronic datalogging of weight, because that sort of geek stuff is what I live for. Since what I planned to do was very similar to how their research hives are set up, I felt justified. But there are also other tricks I've not heard described elsewhere. He puts rectangular corpse traps in front of their hives, elevated off the ground a little and with hardware cloth bottoms (like screened bottom boards, but outside). This gives him a way to count the corpses, examine them to determine life phase, deformations, etc., and do autopsies. That's simple enough to do for any of us.
As for what they say about pesticides, that's an experiment I'm fortunately able to skip. Our lucky bees will have to search far and wide to find any.