I have mixed feelings on Big Al's. I'm sure plenty of their fish are fine, but I've seen quite a few that didn't look great. I once saw clowns with obvious signs of brooklenella, and they were still netting fish out of that tank for a customer. Christy tried to point this out to one of their employees, but they were unconcerned.
If they are now recognizing and labeling sick fish, that's a great improvement. They have always had a good policy of labeling and holding new arrivals.
My bigger reservation to buying fish from Big Al's is just general appearance. There are a few fish I consider to be a canary in a coal mine. The few achilles tangs I've seen there were more brown/tan than black. That's a sure sign of stress and/or poor water quality - trust me, I have some experience with keeping an achilles (lol). Another time when I was looking around, every purple tang they had was drab colored and had HLLE. For these reasons, I've always hesitated to purchase from them.
Back to the original question, you'll be hard pressed to find a LFS that will give an extended guarantee on fish. 10-14 days gives someone ample opportunity to kill a fish, regardless of its initial health. Acclimation procedures, water quality, stress levels, aggression from other fish, getting the new fish to eat, etc. all come into play. Online shops offer arrive alive and guarantees because they have to - it's to make you comfortable shopping with them.
In my mind, it's no different than selling a Hyundai with a 10-year warranty. It doesn't mean the Hyundai is more reliable than a Toyota with just a 4-year warranty. It's just a tool to promote sales.
I would look for one of the LFSs that gets fish trans-shipped directly (not through a local wholesaler), and ask them if they can order one through their suppliers. You may not get it this week, or even this month, but that's your best chance to end up with a healthy specimen. IMO, a fish from a local wholesaler goes through too many systems - too much handling/rebagging, before it gets to you. A fish with minimal handling and direct shipping has the best chance for survival.
Another thing, I can't understate the benefits of QTing, especially with a tang. Losing a $200 fish sucks, but losing a $200 fish and getting your other fish sick is even worse.