Hey, all. How ya been?

I have a question for ya. There might be someone here to offer a tip or two.

A customer of mine comes in the store today. We get to talking about a new printer he bought and about old pictures and, being curious, I asked if he had any older black and white photographs and accompanying negs.

Oh, BOY! He tells me his uncle was among the first liberators of the Dachau concentration camp to arrive and there some photographs and negatives. He just needs to find them. I tell him I would be honored if he would let me make some prints. We talk a while longer and decide upon, contingent on his finding everything, my making some contact prints so that we can look everything over and decide how he/we might like to proceed.

So, if/when I receive these negatives, what should I look for? Other than the generic 'Carefully', how should they be handled? How can I evaluate their condition? I don't want them to crack when I press them in the contact frame against the paper. I wouldn't even dream of cleaning or allowing them to get wet. These are a cherished treasure.