I've been a hobbyist for a very long time, and have seen so many in the hobby come and go because of failures and frustration, and it's sad. It's another reason I made the shop, really to help people and try to change what the typical experience might be.
The best in my mind (at least I'm hoping) long term business strategy is getting people to not leave the hobby and retain them in the long term; some of the industry pro data available says on average it's only about one year for most folks, both freshwater and saltwater included. That's because people end up spending tons of money, their fish end up dying, and they may replace them a few times and the store is happy to keep selling them again, and then they eventually get fed up and there's new people to replace them. You can thank the Petco and PetSmarts for that in the aggregate; unfortunately most of those new aquarists don't even know better and aren't given proper instruction or education. It's both the fish and the longer term aquarists that suffer in the end, with gross mortality that still risks public condemnation of even proper collection practices (e.g. Hawaii).
Even if it doesn't ever make a profit or is feasible in a large scale way, (and I'll try to change that one day, I'm a molecular pathogen engineer by trade, and have a plan), treating the fish is simply the right thing to do, as best you can as possible, so you don't potentially ruin someone's day and kill their pets. I have a conscience - at least a dozen folks in the past two months came to me traumatized, losing every single fish they had to velvet, some for many years, simply because of one small recent addition, and it's absolutely heartbreaking to see people contemplate giving up the entire hobby because of crashes like that.
Even as a pro, it's not that easy necessarily to treat everything out there currently and get it right every time, so it's hard to expect hobbyists to actually do it effectively themselves. There's currently a copper resistant strain of velvet going around, and that's seemingly causing a pandemic. That's from wholesalers keeping constantly low levels of copper in their systems for years, without effectively knocking out every stage of the life cycle, and having constant new fish additions. If it comes from the ocean, it's going to have both ich and velvet on it more than 85% of the time, if it doesn't already get cross contaminated at a supplier level along the half a dozen hands or more hands it may travel through.
I believe it's our job here as the delivery agent of these creatures to not let that get out into the open and to customers' tanks in the first place. I can't guarantee truly pathogen free, bet your life on it clean just fish yet, despite the microscopy verification (until one day when I get time to work on my PCR detection venture), but we do try our hardest to get there as muchbas possible, and my customers that know and trust me are confident that I would truly replace everything should something catastrophic happen at my fault (and everything in that tank were from me), or otherwise gladly take back/re-treat everything again if something snuck through. It's an easy promise to make when it's basically never happened before.