here is an idea which I am going to start putting into practice:

If your selling webhosting, you simply dont send the info to their email but you send it by post (recorded delivery) so you have a tracking number.

If your selling designs and websites then you put the skin onto a cd (less than 1 pound each to buy, not much) and send the cd to their address again by using a (recorded delivery) so you have a tracking number.

You could perhaps give them the info by email if you wanted too but I suggest you still post the info to them, this way you have proof of delivery and acceptance, hence they cannot win a chargeback, unless they try lying.