Let me pose a question...
Regular (10 year) client requests 5 vans at 90 minute intervals beginning at 20:30 and you can only cover 3 of them with your own, or regular subbies because of other prior commitments so you post jobs on Mtvan and get a response from an apparently reputable Courier Co who is able to cover the other 2 jobs at a not inexpensive rate.
Go ahead, the job needs doing.
Later that week the same Courier Co is not available for similar jobs due to regular work... That is how it goes, no probs.
Would you expect to find Courier Co's Jotters & Deskpads littering your client's shipping office just a few weeks later?