There are a lot of fantastic ray keepers here with immense experience on this topic. I am learning the ropes but this is what I have been taught and have learned so far.
1) Purge the rays for 48 hours prior to shipping.
2) Ship in sturdy polyethylene bags, sealed very, very well. Use strong rubber bands or consider using castration bands and tool available from aquatieco.com for example.
3) Ship in the cleanest water possible to you.
4) Triple bag, reversing each bag (open end to factory sealed end)
5) Cover or trim the spine, covering is best, trimming has its place but can be more difficult for the ray and yourself. You decide.
6) Use a sturdy cardboard box with 1/2 inch or more of styrofoam insulation that completely surrounds the bags of water.
7) Use quality heat packs, don't skimp.
Make sure the heat packs have some air space around them so they operate properly and do not let them contact the bag(s). Tape them to the corners of the foam box.
8) Use a small dose of PRIME to add a little insurance to the health of the ray(s).
9) Ship each ray in its own bag(s).
10) Use the ratio 1/3 water, 2/3 oxygen. Not air.
11) Make sure that your customer is priority! Be dead honest about everything. Make sure to honor your word. Make sure they understand what you are or are not capable of.
12) Make sure you have some sort of agreement regarding the arrival of the ray.
*example* Live arrivlal guaranteed. Customer must be present as soon as ray is available for release. If dead, sever the tail from the body. Take digital photo of dead ray minus tail with time stamp and shipping bill in it. Email or call within 2hrs. If dead refund 100, 75, 50, 25%.
(This sounds brutal but is very effective in eliminating fraud)
There is some great literature available online dealing with the this topic. Search for it. Consider Aquabid, you can find a manual for sale there that offers oodles of info. You gotta buy it though. Read the stickies here.
Other ray keepers will chime in here, take their advice to heart. Don't risk yourself, your rays or your customer.
Good luck,
Respectfully submitted,
FireMedic.