I’ve done it but don’t like to.
Wire transfers are cheap ($15-$35 at local banks and credit unions). They are my preferred way of dealing. I even pay for it as buyer or seller! With any sort of paper (bank check, certified check, money order, Travelers Checks, etc.) I’d hold the horse for 7 working days after the first working day after the payment is received before I released custody of the horse.
If you want to be REALLY paranoid remember that counterfeit hundreds are well known in most places. I’ve even seen convenience store clerks use the “reality pens” developed to detect counterfeit money on $5 bills!
There are rules on reporting cash transactions. Here is one article on one set of rules. There may be others:
https://finance.zacks.com/much-can-withdraw-savings-account-being-reported-irs-6446.html
The “underground economy” in agriculture is quite large. Someday the Feds will figure that out and there will be an enforcement push. But, as they say, “so far, so good!”
G.