I go through aquabid a TON. actually 99% of my fish are from there. Make sure you check the feedback rating before you buy, but I've personally only ever had 1 bad experience from a seller. Most sellers dont have a DOA guarentee on priority, but everytime I've had a DOA (which is rare) the seller has offered to replace for just a reshipping charge anyways.
You just have to be careful about what postal system you are using. I have had so many issues with USPS lately that it's rediculous. I always try to get the sellers to use fed-ex 2nd day instead because they are much more dependable and not much more expensive.
hope this helps!!
by the way, I love your discus!!! I've been considering going into them for a while now, but I haven't gotten that far yet.