I've bought logos and some other design stuff on Fiverr - have had mixed results, occasional good stuff.
I've also hired a couple of people to do work through Upwork (when it was oDesk) - I did have some good work done but I was not convinced that the same person was always doing the work, it seemed to me that it was being farmed out from one account that had good ratings.
The best result I have had (but the most pricey thing I have paid for) was design work done by a local agency (https://weare2ndfloor.com/). I spent a lot of time googling, looking at portfolios etc before getting in touch with them, but in the end it was worth it, I am very pleased with what they produced.
