NDD covers both ecn-broker and stp-broker models. The claim is that the broker earns only from commission or markup and is indifferent to whether clients win or lose.
Treat the label sceptically and check the regulator's records instead. Many firms run a hybrid book, sending some clients externally and internalising others, which is disclosed in the terms of business rather than the homepage. See hybrid-book.
Example: a broker's execution policy states that orders may be executed against the firm as principal. That single sentence means the account is not necessarily no dealing desk regardless of what the marketing page says.
Related: ecn-broker, stp-broker, hybrid-book, dealing-desk