How is a stores inventory logged and accounted for

How is a store who has multiple amps of the same brand logged?
If you are asking about inventory control of retail store. Each unique model should have an unique identifier called SKU number assigned to it. SKU stands for Stock Keep Unit. For example, if you have two Brand A model Super100 100Wx2 amps, and four Brand A HT200 200Wx5 amps; your inventory log will show:

SKU# Description Quantity

1ABC Brand A Super100 100Wx2 2
2ABC Brand A HT200 200Wx2 4

I hope this is what you are looking for.
Upscale must not use this
Whoever bought the Cary amp is the one at fault for not checking to see if everything was right. Its been a year and a half. Learn from it and get over it. I've bought from Upscale too and have always had a positive experience.
If I paid for this, and they sent me that, I'd probably send it back right away.
I once purchased a pair of shoes and when I got home, I discovered they put two difference sizes in the box. The simple lesson is when you buy "anything" (including audio equipment), you should check the invoice against the box label. When you get the item home and open it, you should check everything again. Any discrepancies mean an immediate phone call to the store and a return trip to fix the problem. You could also inspect the box at the store (if possible).

The SKU# and serial number should always be checked to ensure you got the right item. While most stores keep accurate inventory controls using sku#s, sometimes mistakes happen. This is why everything needs to be checked before and after the purchase. I hope this helps.