In all reality why would one need a guarantee...A guarantee is more or less a token of good faith on the shops part more than it is a guarantee of health.....If a fish looks healthy, eats and is doing what ts supposed to do when yu buy it, and you acclimate them properly, and have them in a properly maintained setup, there is really no reason they should die within 24 hours or 1 week or 2 weeks.....I like to look at fish i shops even if I am not looking to buy. I like to visit these shops just as they open up espeically after a holiday or weekend especially if the shops are not open on a Sunday etc. You can pretty well get a good idea just how well a fish is according to how well the other tanks are kept and a good visual of all the fish in the other tanks be it fresh or salt..Our main LFS here (strictly SW) has inventory tags on all the tanks with dates fish was received.....sure makes it nice to be able to see when fish came in and how they are doing. If its been there for a week or two there is no reason it should die the next day if bought........at least not because the fish was sick.
I can see somewhat of a warranty on mailorder......as it helps sway a potential purchaser to buy online. Shipping is stressfull, much more than simply bagging the fish at the lfs and carrying it home.......So my view is warranty helps ease any potential for a lose if by chance a fish does not make it during shipping......however a lot of places have a lot of bells and whistles to ring and blow toget satisfaction when they are received dead.......I rather buy at a bit higher price and not have to send bodies back or make a claim within 2 hours of receipt etc.......One place has 14 days......no problems or questions asked, no bodies to return or water samples to send either, Just callem and tell em the fish died and a new one will be sent imediately or a credit issued to your store account or credit card. Thats hard to beat in my opinion.