aquarium maintenance companies charge arms and legs to house customers' fish that the customer already own. Sometimes it is cheaper to buy all those fish all over again.
Dong this isn't exactly true. When I was running a small tank maintenance company while in college all I charged was an extra $10-$15 on top of the fish cost. I would qt them for 3-4 weeks and fatten the fish up before the customer got them. That $10-$15 didn't really make me any extra money considering the food cost, electricity, how often I was doing w/c (salt/rodi water), and delivering the fish. It was more of a service to existing customers I had. It was worth it to me to make sure the customers fish was healthy then to get a phone call from a customer saying his tank broke out in ich.
That being said frank is 100% right about possibly paying an extra 30% more for a qt'd fish. Think about it. A LFS would have to pay for the fish, ship it here, ensure it is eating which in itself could take a week or so, deal with deaths from other fish/coral in the order (they obviously have to make some of that money back by charging a bit more for the fish that lived), and then sit on the fish for a month while making $0. Hard for a business to do that. That being said, I don't think any of our sponsors would knowingly sell a sick/distressed fish to a customer because of fear of driving the customer base away not to mention it's not fair to the livestock.