I've done quite a few custom orders in my time, mostly single color changes and simple adjustments. Sometimes I get one that hurts my head a little and here's a breakdown of what happens in my head during that kind of custom order.
First, the request:
What they said: Could you make this design in purple and green?
What I heard: I have no idea how you make this item, but I assume it's magic and can be done anyway I like.
What I said: Sure I'll make that up right away.
What I meant: Hell, if I know, but I'll sure try.
Then the creation:
I will spend the next two hour agonizing over how to do this. Then I'll probably make three or so failed attempts before succeeding. I will then spend a hour just staring at the piece thinking, 'is this alright and will she like it?'. I'll take pictures and then debate actually sending said pictures.
Then I present my photos of the piece to the customer. This is accompanied by extreme anxiety and fear that after all my hard work, the product will be dismissed as "not what they wanted".
What they say: Wow, it's beautiful. I can't wait to get it
What I hear: Looks alright, I'll let you know when I get it.
I pack up the order and send it out as quickly as possible. Then I wait and wait for the feedback to arrive, terrified that the second they open the package, they'll realize what a hack I am and send it right back.
What they say: I love it! Thanks so much, I can't wait to wear it!
What I hear: Thanks for your time, maybe you'll get right in the future.
I'm not really that hard on myself, but I would be lying if I said I didn't doubt myself on a regular basis. I do love custom orders though, they allow me to stretch myself as an artist. They make me think outside the box and play with colors, which I tend to avoid. Of course I already screwed up this custom order and have to make another. That'll teach me to watch my DVR'd comedies whilst tatting.