I'd have thought the main starting point was the Para Handy stories by Neil Munro, written in 1905-1923 about the crew of the Vital Spark, a small, scruffy Scottish commercial steamboat. CJ Cherryh used the idea in some of her SF novels, although I'm not sure if any of them pre-dates the first Star Wars film or not. The Chanur series, for example, first came out in 1981, so she was writing the first Chanur book round about the time Star Wars came out and we don't know who first had the idea of a furry crew flying a commercial ship so decrepit that bits of it had to be kicked to make them work.
I think some of Andre Norton's stories might qualify, and they definitely do predate Star Wars. Star Rangers, for example, written in 1953, opens with the crew nursing their limping ship to a crash landing, although in that case it's a warship rather than a trader. Her Postmarked the Stars series involves the crew of a small commercial ship which, if not quite falling apart, is certainly operating on a shoestring.