I feel your pain. You can't help some people. My brother and his wife bought my twelve year old nephew a Corn hatchling. I carefully wrote them a basic caresheet, helped them get the setup right and they dutifully bought Kathy's book.
They've now changed the UTH for a heat lamp, they have the stat probe half way up the wall of the tank at the cool end and they're powerfeeding (the poor Corn was adult-sized at less than a year old). All because "The Man In The Shop" told them I'd given them wrong information. They claim to have ready Kathy's book but apparently *she* knows less than "The Man In The Shop" as well.
When the snake stopped eating earlier in the year, "TMITS" told them that it was in a breeding fast. At seven months old. Yeah right. I told them to check the temps and was told without a pause that they were fine. When I went round, the UTH had been accidentally switched off at the plug and the temp was down to under 70 degrees (not that their plastic dial thermometer - that I had begged them to change - had even twitched of course. ARRRGGHHH!). I switched the UTH back on and stood over it while the stat brought it back to 85 degrees. Two days later the snake started eating again. However, they still firmly believe that it was because it had ended its breeding fast.
Ultimately, people choose who they believe and what research they do for themselves, and you can't do much about it.