Leave a 2nd class stamped envelope, always have and it works a treat, most of my customers are a long way away and to collect would be a nightmare.
Of course I do have a few who always forget, so mark them on George and collect next time I am working in the area, on the whole its a brilliant way of getting paid for me.
A few customers are now offering to pay online and this is even better, switch on the computer and there is a payment.