It’s simple. You must receive a receipt that specifies as many details about your jewelry as possible, like:
Type of metal: They should note 14k yellow/white gold, 18k, platinum, sterling silver, gold-plated, etc. If they just put “gold color” down, ask them to test it for type of gold and have them note if it’s 14k or 18k.
Length of chain: Iif it’s a necklace or bracelet, they should measure it and put the exact length.
Weight of the piece: They should have a scale and put the piece on the scale and note the exact gram or dwt (“pennyweight”) on the receipt
Gemstones: Ask the jeweler to note the type of stone (ruby, diamond, sapphire). If they only want to put the color of the stone (red, clear, blue) ask if there’s someone on hand who can specify it because if you are leaving a genuine gemstone, you want to receive a genuine gemstone back (or replace it with a genuine gemstone if their store burns down, is robbed, etc) They should measure each stone with a millimeter gauge and note the size. They can’t write down the weight because the stones are set, unless you bring in a loose one, then it can be weighed and recorded.
Diamonds: This is the most important part. Every diamond, unless it is flawless which is extremely rare, has some internal characteristics (or flaws) in it. Ask the jeweler to “map” your diamond on the receipt. That means s/he will look at the diamond through magnification and note on the receipt where the identifying characteristics are and what they look like (feather, included crystals, etc). The diamond should also be measured very exactly with a Leveridge gauge to have the millimeter length of the diameter recorded (two diameters is best because a diamond is often not perfectly circular in circumference). Then after the diamond is mapped on the receipt, ask the jeweler to show you your diamond under magnification and be sure you can identify the marks s/he made on the receipt as being in the diamond. When you pick up your diamond after the repair or appraisal is complete, ask the jeweler to show you your diamond again under magnification so you can again identify the internal characteristics of the diamond and know that it is yours.
Other descriptions: The jeweler should note any problems when they take your piece in (like the surface of the gemstone is scratched or the necklace is broken or the finish has been affected in some way) so that you know these imperfections existed when you dropped it off. When you pick it up, it will be cleaned and you will look at it closely, probably more closely than you did when you dropped it off so those imperfections might become obvious to you then. That’s why it’s important the jeweler note them on intake so you don’t think they occurred after you dropped your piece off.
Insured Value: The jeweler will assign an insured value to your piece while it’s there. That protects you and gives you coverage in the unlikely event that his/her store is robbed while your piece is there, or it suffers a fire or some other catastrophe. The jeweler will have insurance to cover this so you need to be sure you are satisfied with the value s/he assigns to your piece while in their possession.