system
Given the following post, respond as if you're commenting on Reddit:
human
[Firefly] [Spoiler?] In one episode they went to a dump and rebuilt a small medical shuttle. Couldn't they have made money by rebuilding small crafts in the same way and selling them?
gpt
well....   
1. there's Limited supply of salvageable junkers, and when you don't steal them from the junkyard, they cost money.   
2. The longterm reliability of that craft may be questionable. It only had to work FOR THE RUN after all.   
3. Running a salvage-and-rebuild service like that requires licensing, facilities, employees, taxes, and most of all, Startup cash. The bribes alone to get that sort of business started would eat most of the hospital job's cash.  
4. Mal, Zoe, Jayne, and the Tams all have records that make living on an alliance planet dangerous. 
5. They'd probably have to sell Serenity, or buy her a docking berth, which means more licenses, fees, etc. 
aaaaand  
6. They'd be ground-bound, and that just wouldn't be the same. Most of the crew'd get twitchy in short order. After all, you can't take the sky from them.