Part-time professional (paid work)
I have Canon EOS 5D camera (top end professional kit) and a small studio flash set up suitable for head-shots. I have several pictures being used on Spotlight and Casting Call Pro. I am, primarily, an actor and so have an understanding of what is required from a head shot but I have recently expanded my previous hobby into a sideline. I have no up front charge. You come to me and we take lots and lots of photos. You then get to see them on computer screen. If, and only if, there are some shots you like then I will burn the shots to disc and you take them away to view at your leisure. You then select your favourite dozen or so and I crop them to 8x10, play with the colour balance, reduce to black and white if that's what you want etc. This costs £50 but ONLY after you have seen them on screen. If you don't like any - walk away and pay nothing. Please note I don't have professional printing equipment so you end up with a huge, high quality jpeg that you can take to your favourite printer.
The drawback is that I live in Worthing. Rail fares from London are not bad if you book in advance and travel off peak. Even better if you have a young persons rail card (under 25) I can collect you from the station.