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.
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.