Verifying Executor of a Estate

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I am in NC and have a house on the market. A local agent brought a cash offer from a buyer which is very attractive. I have verbally indicated that I will accept the offer provided the buyer produces proof of funds. Here is what the agent said..

"The buyer is getting money from the estate of her dad who was a resident of CA. The executor is sending over a letter, copy of the bank statement showing the funds, and copy of paper work showing he is executor"

How do I verify that the Executor is legit and the documents show that the funds are available? I read somewhere that "in CA the executor needs to be confirmed by a probate court before he can carry out his duties. The court gives the executor official documents that confirm the executor's authority to act on behalf of the estate". Can I call the clerk of court in CA to confirm ?