Most, if not all, banks stopped providing "certified" checks some time ago. A certified check (assuming it was not counterfeit) was a way a bank verified that sufficient funds were in the account to satisfy the notes obligation when tendered back to the bank by the payee. The bank checked the balance in account at the time the check/note was issue and then would hold those funds in the account until the check was tendered to the bank for payment. So long as the check was not counterfeit, it was as good as cash.
However, these days, most banks, if not all, will only issue "cashiers" checks. A cashiers check only means that there are sufficient funds in the account to cover the amount of the check at the time the check is issued. Ten minutes after asking for a cashiers check, the person whose name is on the bank account can come in and withdraw all the funds from the account and the cashiers check becomes as worthless as any other check drawn on an account with no funds.
The advise on a bill of sale is good. The advise regarding getting cash is good. The advise regarding dealing with honest people in that honest people don't mind getting cash and doing the right thing is good. The advise regarding calling the bank to verify that funds are in the account doesn't really work. If the buyer is a conman, they can hand you the check, you call to verify the funds, get verification, give the con the tractor and before the con leaves your neighborhood a joint account holder can withdraw all the funds making your check worthless. There are a lot of other ways to do it, but calling to verify that funds are in the account will not prevent a worthless check.
