My best advice for sole traders is do not spread yourself to thin, get say max 3/4 regular users of your service see how that pans out over a month... Then make sure you support the supplier who is consistently supplying you work at a decent rate and payment terms... You will then build up a strong reliable relationship and know where your bread is buttered and that the grass is not always greener!
Remember you are one man and a van don't promise the earth to everyone...