"Wrecked" by Therese Greenwood, in Ellery Queen's Mystery Magazine, March/April 2012.
The narrator is Rosie, who runs a small-town auto wrecker. She's interesting in her own way, with her fatalism about her business and her pride in her nephew the cop who was "the grade-two knock-knock joke champion of St. Paul's school." And there is her mechanic Gary, who can't stop being snotty to that same cop, no matter how ill-advised his attitude is, or how bad his jokes are.
When a murdered man is found in the car crushing machinery Rosie will need help from all these characters to catch the bad guy.