We have a customer that has notified us she sold a large tract of RE and wants to wire in $1,000,000 then withdraw the same amount in cash. She is a well off customer, with several accounts and trusts, etc. But this still seems off. Is there a way we can refuse?

Sure, you can. You are under no such obligation to disburse that much cash to anyone.

I believe you - you've always provided top notch answers, but I have to ask. Is there a source or citation or anything I can look at to substantiate a refusal? I'm out of my depths here.,

You may look in your deposit terms and conditions.

Handing out lots of cash was a topic of conversation at the beginning of COVID. Here is one post that discussed limiting cash:

https://www.bankersonline.com/forum/ubbthreads.php/ubb/showflat/Number/2233235/Searchpage/1/Main/266864/Words/%22limiting+cash%22/Search/true/re-limitation-on-withdraw-of-large-cash-during-crisis#Post2233235

Look for something like this: ARE THERE SPECIAL RULES IF YOU WANT TO MAKE A LARGE CASH WITHDRAWAL OR DEPOSIT?
We may place reasonable restrictions on a large cash withdrawal or check-cashing or refuse a request for such transactions. These
restrictions include requiring you or your payee to provide reasonable advance notice. We do not have any obligation to provide
security if you or your payee receive a significant amount of cash. If you want to deposit or withdraw cash for a large amount, we
have the right to require you to provide adequate and acceptable security at your expense, as well as, sign a Letter of Indemnification.

If you do not have anything like this in your agreement, contact your legal counsel. I would also charge them for the extra branch security that will be required and the shipment costs, if you do it.

Thank you both!!!

Hand her the "Currency Transaction Reports and Cash Purchases of Negotiable Instruments" FACTS YOU SHOULD KNOW pamphlet (does anyone still use these?); that should stop her dead in her tracks.

We had a customer in our El Paso area that was getting high 6 figures and wanted cash. We did all we could to dissuade him and we had our security escort him as far as the door and then he was on his own. This was an in-store branch so the parking lot wasn't ours but you can hear them screaming for their money if they got robbed. I would likewise emphasize that they not talk to others unless absolutely necessary about what they were doing, or when and where. IMHO this person needs reminding as walking with that cash is irresponsible so they're not as high up the food chain as they may believe. I think it's equally irresponsible to give that much cash to someone else for any reputable transaction.