What they said, really.
Bamboo - what you'd have got at B&Q and what he may have had - is hollow and has a horrible tendency to split, leaving very sharp edges.
Canes for BDSM use need to be solid, typically rattan. This has a spongy-like core if you look at one end, made up of lots of small tubes. Although you can break them, they're much stronger and can be very flexible, especially when wet.
Thinner ones sting and welt more than thicker ones which are more 'thuddy' and bruisey. Individual bottoms tend to have definite preferences over which is more enjoyable.
Floppier canes typically hurt/sting more - although the top should be aiming things so that the actual end doesn't hit the bottom, the flexibility means that the far end can be going much faster when it comes into contact. (This, plus the added weight of the water absorbed again increasing the force of the impact, is why some people soak them for twenty minutes or so before use.)
Caning can leave all sorts of marks, depending on width and strength of strokes. To minimise them, a spanking and/or paddling reddening the bottom first is definitely advisable.
As ever, what you charge is up to you, but dedicated pro-subs either usually charge a lot more than £5/stroke or far more per hour and have limits on how many can happen in that time. Because of the danger of having an random stranger with a cane in his hand doing stuff to you, they can also insist on having someone else around too - chargeable to the client, obviously.