Just so I am clear, he wants to be able to enter the string "POA" for the price instead of a number?
If you are using a payment gateway to process the transactions, this will cause issues, the payment gateways will fail if a string is passed for the price.
This is not a change we can offer support for, in addition to removing the validation, you would need to edit the products table of the database to change the price column to allow text, and also edit the insert record behavior to pass the price as a text instead of a number.
you would be better off just entering the price as 0 and adding "Price On Asking" to the product name or description.