I've had surprisingly good luck with Amazon over the past couple of years. I've had records from Craft Recordings, Blue Note, and a handful of others, and they've been double-boxed and at worst, might have had a very small "dish" warp. I've had a few third party seller purchases, but they have all been from existing large-scale dealers who themselves know how to pack records.
When they first started selling vinyl though, they had no idea what they were selling. It was not uncommon to find an LP dropped into a flat box which it would fit on the diagonal, with an other heavy item or two dumped in. I did my share of returns back then. I also had some come from Amazon in Europe and not only did I get the poorly packed records, DHL proceeded to shred the box en route. That is, when DHL even delivered--I had my share of packages from the EU in DHL's hands that arrived either a month after ordering, or never show up at all.
Heat is the #2 reason I ask all carriers to deliver to the side door--it is shaded, whereas during the month or so of summer sunlight that hits the north side of the house, it can get awfully roasty out there.