The heat issue of shipping in the summer is mostly a function of a few simple things: 1) how mature the plant is. A rooted cutting is more susceptible to stress than a one year old plant that is well established. 2) whether the plant is delivered and left in the sun, or not. 3) how well watered it was before it was shipped. Was it watered well the day before and allowed to become fully hydated? Was it re-watered just be shipping?
I had some plants shipped from San Diego to NY and back (shipping address snafu), so they were gone for 12 days and they were fine. Put them in the shade and watered them well and reshipped them the following Monday.
Summer heat can lead to problems, and stuff happens, but if done properly, it is doable.
Wills, Thanx for the pix. I know I have some somewhere, but not at the ready. The string "thing" works fine, as well. Again, as long as the weight is controlled, the rest will take care of itself.
FYI, packing peanuts do NOT control the weight, they just reduce the amount of the pot can move. There will always be some settling during shipment, and then the weight is loose and the leaves and stems are now in contact with material which can rub against them and damage them.