The problems with outsourcing are :
No control over quality
Increased turnaround time
Increased cost
All of these will put people off using you. When you say printing other peoples designs do you mean making them for companies etc... of their logo? Look on Ebay for your country and see how cheap people are bulk printing decals now. Most of them are making next to nothing on an order and that is with printing them on their own equipment.
Unless you can design for people as well and do custom work on your own printer, then it really isn't worth it. Most people doing this sort of work have shops and do it for local customers which is how they get the work.
Sorry, but I have to disagree with all of those points.
Well known trade suppliers have very nice equipment and use high quality materials. A supplier's ability to produce consistent quality and turn jobs out fast is 100% critical to their business model. Understanding color management, calibrating equipment / software, optimizing production workflows, logistical operations, not to mention raw buying power for materials and lower shipping rates. There are so many things going on behind the scenes.
If someone hopes to buy a cheap printer, plotter and laminator (e.g. $20-25k for
very basic entry level gear) and source generic materials to save a few bucks -- quality control is going to be an everyday problem. Not to mention how much more expensive the consumables are (like eco-solvent inks and buying films 1 roll at a time)
Most suppliers will have an order at your doorstep within 2 business days, which is nearly as fast as in-house production (considering things like outgassing time and such). I've been in the biz for 26 years. I have a lot of nice equipment -- and I still outsource jobs when I'm slammed with work. If you know the capabilities of your supplier -- provided you know how to set up your artwork correctly -- you'll know exactly what kind of quality to expect.
Increased cost? Not unless you acquired a
sign shop and all their equipment / consumables for free. Let's say a company is providing you a nice quality vinyl, printed on an HP Scitex, gloss laminated, and contour cut for $3.50-4/sq.ft. You might be thinking, okay. Hypothetically, let's say the material cost is 1/3 of that. I want to put that other 2/3 in my pocket -- but it doesn't work like that. Equipment cost, maintenance, software, utilities, labor and other overhead will wipe that out in a heartbeat. You need a lot of steady volume to justify in-house production, especially if you're just focused on "stickers". With outsourcing, there's very little risk and you can spend a lot more time on marketing.
A potential customer that already buys online -- they're already familiar with "bottom dollar" pricing. Unless they're willing to pay extra for "keeping business local", it's going to be very difficult to make money off them. You really need to do something different to stand out because this industry is super saturated with low ballers.
If you can't mark up the products you buy from a trade supplier to make it worthwhile, you're doing something very wrong.