Thought i'd chip in with advice from some hard lessons learned when starting out

* Make sure you cover costs if replacements are needed including postage and the pick up collection of supposed 'substandard' mugs
* Make sure Samples are identical, one for you and for customer and photograph the customers sample
* VERY IMPORTANT *****Clearly state your T&Cs with quote/proforma*****
* Do not spend the money received before customer receives their order and is happy, Especially on large orders, You really do not want to be up the 'creek' if they requests a full refund and you have spent the dough
* Check and double check every order before packaging it.

Finally realise sometimes that there is no pleasing a customer. Regardless. Take the hit, Learn and move on.

This has brought up bad memories, I'm off for a beer!