I was just reading in the etsy forums about an etsy seller that is being taken advantage of, and I have to admit, I have had the same thing happen to me in my shop.
A couple of months ago I had some contact me about one of my bracelets. She said she was looking for a gift for one of her family members, and really liked one that was in my sold items. She asked me to take apart the bracelet and make her a necklace which I did without problem. It was in my early days when sales were more sparse and I was happy for the potential sale.
So I took apart the bracelet and made it into the necklace. I took pics of it for her, and sent her a message. Needless to say, it wasn't what she wanted. So I took it apart again, and made it less asymmetrical as she requested. Took pics again, and posted them in a message to her. Once again she wasn't happy. She wanted the one I had sold a few weeks prior, but I just couldn't make that particular necklace for her because I didn't have enough supplies.
After nearly 10 convos back and forth she ended up getting rude with me about it, and telling me she didn't want the necklace after all. I was so upset, first that what I made wasn't good enough they way it was, and second because after trying so hard to get that sale, and literally spending about 3 hours trying to make it right, she had declined what I had made for her. Basically I had worked approximately 4 hours including convos, photos, editing, and messaging for nothing.
The moral of this story? Be sure to get you get at LEAST 50% (non-refundable) payment up front for your item before doing any custom order or custom work. Even if they don't end up buying the piece, your time is still valuable.
Above is the infamous bracelet. It really needs a good home!