Custom Orders

As much as things are a little busy in the studio these days with one order of one item, I have been doing a wee bit of custom work for people to shake things up a bit for myself. 
Custom work is tricky- I always have to make an extra set or item because something generally goes wrong.  I also only take on custom orders if the work is in line with what I'm already making so I'm not having to re-invent the wheel (no pun intended;).  When the order turns out well, it's a refreshing change from what usually happens, which is that it takes me twice as long to complete an order.  I know a lot of people charge double for custom work, (because of the extra time involved), and I sometimes charge more because it might be a new glaze I've got to test or new forms I have to develop for the order, however most often I use the opportunity to experiment within my regular body of work.  And often I end up liking how things turn out.
How do you feel about custom orders if you get requests?  Do you feel that you have to charge a lot extra for them?
I hope you have a great weekend! I'm hoping to finally up-date my online shops to include some of the work that made it home from Renegade.  And hopefully we'll start feeling like summer in our neck of the woods:)!