My only piece of advice is to do EXACTLY what you say you will, when you promise to do it. Read that again, and if you need to, post it on your work bench to remind yourself daily.
If you have decisions to make while working on someones gun(s), it'd serve you well to remember they are NOT your decisions to make, they are your customers, so CALL AND ASK THEM so the customer can direct you to do what he WANTS DONE, not what you want done. Remember, you work for them, on THEIR property, it's not yours to ruin. Your job is to modify something that DOES NOT BELONG TO YOU, and is not yours to dick with beyond what you are given permission to dick with it. Hopefully you can read this loud and clear and understand where most problems arise when dealing with gunsmiths.
The cost is less important than the above to people that have dealt with gunsmiths before.
