Glad you asked. Everything seems within "the law", but they bill the absolute maximum allowed. For example, my CPAP machine was billed in monthly installments to my insurance. The total cost of the machine was, and I don't remember exactly, about 2-3 times what the cost was on a CPAP webpage bought outright. I'm sure the DME and insurance (or Medicare/Medicaid) have an agreement, but It just rubbed me the wrong way that they were charging way over "retail". It's like paying window sticker price for a car, plus a significant mark up. They email me asking if I want mask replacements every quarter. That is what "the law allows", but I don't need replacements that often. With a minimum of care the masks should last much longer than the replacement schedule "recommended" by the DME.
Again, I am sure it's all within the insurance/DME agreement, but this is part of the reason that insurance and medical expenses are so high. Most people don't pay attention, and/or "do whatever they are told by a medical professional", so up go the expenses. Just my 2 cents. Don't want to get too cloak roomish.