Jacky,
Your listing should be your contract with your customer and written as such. As a Custom Listing needs to have guidelines and time frames that are clear and exacting to save Both Parties time and misunderstandings.
I learned the hard way too, so I certainly understand the frustrations.
I gladly share a link from one of my sold Custom Listing items that is public to anyone who searches. I hope this example of verbiage/presentation is helpful. Also note that in this instance, the customers color choice did not end up red, they ended up blue:) When I painted the prototype the color the customer originally wanted, I knew immediately that it would not work; so, I painted the design she wanted also in an alternate color I felt worked. She loved my alternate and we went with that. I was still out time, but it sure did make my day to escape what could have been costly in many ways.
(sometimes customers don't know that what they want will not work so they need an out:)
https://www.etsy.com/transaction/88754147Best always+++
Deborah
Skyspirit8Studios