English Translation
I am in the grocery line.
As in, “my line of work is selling groceries,” not “I’m standing in line to purchase groceries,” correct?
@cstuartroe
You are partially correct. The speaker is not a customer but a dealer.
○○商をやっている is most likely to mean “As a business owner, I run trading business specializing in groceries.” The speaker is not an employee but an employer, freelancer or entrepreneur. The business is not B2C (a grocery shop selling groceries to customers) but B2B (importing F&B etc. as a wholesaler.)
I am in the grocery line should be:
私は食料品店のレジに並んでいます。or
私はスーパーのレジで並んでいます。
レジ is a loan word from English “cash register”. 食料品店 is a correct phrase but スーパー (meaning: supermarket or mom-and-pop store selling groceries) is more common. Particle に and で are interchangeable with no significant difference.