Is there a way to find the vendor's default payment method (Check, ACH, Wire etc) ?
I don't know where you would entered their default payment method in the AP module.
You could take a field like Location ID under the Defaults tab to enter something like ACH , ect but that info wouldn't pop up anywhere.
You could use the Vendor class to note payment method if you are not using it for something else.
Other Microsoft Sites
I'm a Customer
I'm a Partner
Follow Microsoft Dynamics