customerID = customer.get("contact_id");
companyName = customer.get("company_name");
organizationID = organization.get("organization_id");
ret = zoho.books.getRecords("Estimates", organizationID,"customer_id="+customerID,"zoks");
info ret;

This is how I can check whether a customer has quote or not. This is not a complete code,but a small part of it.