Selling and shipping fish is not an easy business. You are dealing with live animals that need special care in transport. The biggest problem is that no shipper will guarantee live arrival nor will they insure for that. I have shipped USPS, FedEx and UPS. All are the same in this respect. The only guaranteed they differ is to deliver on time and to refund the shipping cost if they do not.
If is important to realize that almost any fish any of us buys or acquires as a gift trade or rescue, had been shipped at least once and often a number of times. I have personally received shipments from as far away as Indonesia. Would you believe a shipments which contained 328 zebra plecos arrived 100% alive? When healthy fish are packed properly and shipped on time, the odds are good there will be few or no losses.
However, as somebody who ships fish which are born in my tanks that there is a need to price in the potential for losses due to carrier issues not fish health or packing issues. However, I am a buyer more than a seller. So I have received a lot of shipped in fish. I expect to cover losses on what I send and to be made whole on those I received DOA. I honor my guarantees and most times so have those I from whom I buy.
What is most important in this process is the seller. It is up to the seller to make good on guarantees or to state there are none before the sale is made. That means the buyer has to do their homework re sellers. More often than not the sellers who do not honor their guarantees are home based hobby sellers or smaller scale sellers who buy wholesale or imported on a smaller scale. They are neither mentally nor financially prepared for haveing a serious problem where fish are lost and the seller will lose a lot to make it right.
Here is the thing to understand about buying fish which must be shipped to you. Quality matters. The best way I can put it is that one live fish has to be worth more than 3 DOAs. Bargain shop and you may get what you paid for and you may not be so happy.
One last observation about buying from sites like AquaBid or smaller scale home based sellers. They may have an excellent reputation, great feedback etc. But if they have sudden issues in their personal lives which will cause their fish stuff to go down the tubes, we as buyers have no way to know that until our box either never arrives or does so filled with DOAS and then the seller stops responding to our request to make it right as promised. most people whill gladly screw you before taking the hit themself.
A going business like Wetspot has a reputation to protect. They are not going to fold their tent and vanish into the night because a fish arrives DOA and they have to replace it. Another good source for healthy fish are at fish clubs. The fish are usually cheaper than retail and healthier as well. <ost hobbyists who are members in a local fish club are responsible fish keepers and they will have healthy stock born in their tanks.