Employing is the way forward, but when i did it you have to trial at least 10 blokes to get 1 decent one.
Then theres the worry of leaving them on their own, do you have time to check their work afterwards and before you collect?
I,m with Tosh on this one, sub it out, at least its partially their work if it goes pear shaped, and you're happy in the knowledge youve sold rounds before therefore you're going to gain more work in the future.
Plus it makes them responsible for their own NIC, Pension, Hols etc: