Difficult to advise, without the following.
1. weight of gold
2. price you have quoted to do the work,
3. Is the client near you
4. Have you the kit hot enough to melt that quantity
5. Do you plan to cast or just roll the ingot to rod or sheet
6.can you roll this quantity of gold ie is your mill up to it
7. do you normally work in white gold.
Then get the customer to watch you melt it and say it has to be at their risk, if it fails it can only go for refining.
If they agree, ok, if the dont agree turn the work down.
how many other jewellers have they been to before you?
They wont say.