Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE customer ( cust_id text, cust_name text, acc_type text, acc_bal number, no_of_loans number, credit_score number, branch_id number, state text )
TABLE: CREATE TABLE bank ( branch_id number, bname text, no_of_customers number, city text, state text )
TABLE: CREATE TABLE loan ( loan_id text, loan_type text, cust_id text, branch_id text, amount number )

### Question ###
What is the average credit score for customers who have never taken a loan?

### Accurate SQL ###

SELECT AVG(credit_score) FROM customer WHERE NOT cust_id IN (SELECT cust_id FROM loan)