Answer by
LeheckaG (1826)
A "purchasing agent" (boss) or "buyer" (grunt) is "someone who shops on behalf of shops".
A "retail (marketing and) merchandise management consultant" works on behalf of manufacturers and/or distributors and BROKERS deals with retailers. They either SELL product or BUY/PURCHASE "retail-shelf-space" depending on how you look at it.
Realize that in larger-chains/stores manufacturers buy/lease retail-shelf-space & retailers receive inventory on-consignment.