Ask an owner what their cost of goods is and most will give you one number for the whole practice. That number is worse than useless — it's actively misleading, because it averages together service lines with completely different economics and hands you a single figure that can be wrong in several directions at the same time. A strong injectable margin can hide a device line drowning in consumables. A healthy blend can disguise a skincare shelf that's quietly become dead inventory. The practice that can't separate its injectable COGS from its skincare COGS is flying on the one instrument guaranteed to lie: the blend.
The fix is to set and track cost-of-goods targets by service line, because only at the line level does COGS become a diagnostic instead of a fog.