Hearing someone say that they saw someone at a fish store doing the surgery SCARES me. That surgery is possible - but does not have a high success rate - and it is SO easy to mess up and kill the fish. There are some big veins right down there - as well as delicate internal organs. You need to really know what you are doing. A "fish store guy" who does something, then sells the fish to an unsuspecting client will have a VERY unhappy client!!!! I consider it unscrupulous. Post op requires strict cleanliness - and removal of stitches. It is not something for a community tank in a store.
Pushing ballast into the body of the fish is a delicate procedure - if you get too much, the fish sinks... if you get too little, it does not work. If it slides to one side or the other, the fish is a side sitter. Even after the surgery, most fish will bottom sit - and only some will be able to regain bouyancy.
I have one fish that was brought to me recently that is a prime candidate, but I have decided that I am not going to do it. I have never seen or even heard of a fish that had this be a long term solution - it simply does not work for long in my experience.