No Prepayment
It's so very simple. You pay your London Walks guide when you turn up for the London Walk you want to go on.
 
If someone's trying to get you to prepay they're not London Walks.
 
Yes, that's a seriously big Caveat Emptor!
 
This all-important matter has of course been thrown into sharp relief by the weather right now! (I'm writing this on January 8, 2010.) It's how do you like your Anchorage Walks? Sure, we're doing them – famously, London Walks take place come hell or high water or arctic temperatures or whatever – but it's we few, we happy few braving the elements. E.G., there were five people on my Kensington Walk yesterday; six on Old Hampstead Village on Wednesday, etc. Well, you get the picture.
 
The point being that over the course of this cold snap – and they're saying we could be in for a fortnight of it – there will be hundreds of potential walkers who'll think better of it – "was going to go on this or that walk, but not in this weather thank you very much". And they'll make the switch to Plan B or Plan C or whatever. 
 
And most important of all, they won't be out a sou. Won't be out a sou because they haven't "booked" and prepaid. With London Walks there's no booking*, no prepayment.
 
Whereas if you prepay – "hey, got a great deal for you...you get to pay pal long before it happens!" – and then can't face going on the walk you've already paid for, can't face going on it because it's sub-zero temperatures and glare ice, well, you don't need a weatherman to see which way that "financial wind" is blowing!
 
Bottom line. Bottom line, indeed. Our way of doing it is better. That's in addition to guiding them better**, of course!
 
*Well, private walks for groups of course have to be booked but even with a booked private walk if the weather is impossible London Walks will always come through for you – the walk can be rescheduled when it's halcyon days!
 
**Not only is the proof in the pudding, it's also on Youtube! Here. And here. And here. Etc. Etc. Etc.