I used to do print brokering many years ago. A couple of thoughts.
– You can make some extra money, but it also takes time to source vendors, get quotes, manage the printing, etc.
– With the rise of online printers, it’s tougher to make money with print brokering. Clients can do a quick search and see all of these places that will print their cards (or whatever) for some pretty low prices. So it’s tougher (though not impossible) to make decent money with it.
– The way my business has evolved, my clients have printers they already work with. So I haven’t been in the position to do any brokering. And I’m okay with that. The liability for the printer’s bill falls on you when brokering.