For small amounts of cash, it's not a problem. But any cash transaction over $10k must be reported. [1] (Structuring your transactions so as to sneak under the limit is illegal.) The same goes for traveling across a US border with over $10k in cash or cash equivalent.
Even under that level, though, some level of suspicion attaches to large wads of cash. I've had vendors ask for cash payment for things in the $1-5k range, and it was pretty clear to me that they had tax evasion in mind.
Even under that level, though, some level of suspicion attaches to large wads of cash. I've had vendors ask for cash payment for things in the $1-5k range, and it was pretty clear to me that they had tax evasion in mind.
[1] https://en.wikipedia.org/wiki/Currency_transaction_report