I would like to get an expensive ring appraised but do not trust a jeweler to hold on to it. What can I do?

I do not trust a jeweler to not take the ring, say they never received it, or switch out the stones. What options do I have to get it appraised? Can I write a letter indicating that the jeweler received the ring and have them sign off on it? Would this be enough evidence in case something were to happen?