These are excellent questions. They do, however, require an extended answer, for which I apologize. The simple part is who is a candidate. The answer is anyone with under eye volume deficit, either from a congenital variation in the area or from volume loss from natural aging or weight loss without significant excess skin. The confusion as how to improve the area and why there are so many problems goes back to when we first started using fillers. At first we had collagen fillers followed in 2002 by Restylane and in 2003 Juvederm Ultra. These were mainly used in the nasolabial lines and similar areas. As we got bolder, we started treating the under eye similar to what we had done elsewhere. This worked some of the time and gave us hope, but frequently produced more swelling than it corrected. Since Restylane tended to cause less swelling, we at first assumed it was the filler. However, we eventually learned that it was where we were injecting the filler, superficially above the orbital ligament. This placement obstructs the lymphatics, the fine vessels that drain fluid from the tissues, thus causing abnormal swelling. In 2005, when Radiesse, a heavy filler, became available, I and a number of other injectors began using it deep on the bone or muscle below the ligament, elevating the ligament and the surface tissues erasing the depression. I was told I was "crazy." However, when I switched back to what everyone else was doing, I again got problems, so I resumed using Radiesse. In 2015, Allergen introduced Juvederm Voluma another heavy filler. They had done research on the proper placement and suggested that it be placed deep and below the ligament. This is how those of us using Radiesse were injecting. It corrects the problem and does not obstruct the lymphatics. It is also safer in other ways. In spite of this, since most injectors were injecting a light filler above the ligament superficially because of habit or because that is what they were initially taught, they continued to use that antiquated method. You may ask "why?" It is because even physicians are slow to change. Even today, almost 7 years after Allergen began teaching the proper technique, probably 90% of injectors still use the wrong method. In fact, studies have shown that it usually takes up to 13 years after a discovery for it to be widely adopted. This means you need to educate yourself about the qualifications and methods used of whoever you see for treatment as you sound like an excellent candidate in the right hands.