There are no "general retailers".
Instead, there are booksellers, grocers, menswear retailers, lumber dealers, online retailers, gift stores, and on and on. 

The North American Industrial Classification System (NAICS) identifies over 50 separate retail segments, each of which sells its own type of merchandise (see below).  And, each of these retail segments has its own financial performance benchmarks: profit margins, inventory turnover, etc.

Clicking on any of the specific retail segment links below will take you to that segment's page at The Retail Owners Institute® website.  There you will find Performance Benchmarks for six Key Ratios for that retail segment, plus much more information.