In the old days of fully refundable (or at least full credit)tickets and more easily obtainable award seats, I knew of a couple of unscrupulous consultants who did this regularly.

Here are the issues: Even a $900 ticket is probably non-refundable and has a change penalty these days. You will lose that right off the top. Since it was booked through a travel agent, they may get a record of tickets actually used since it may affect the booking fees they charge. The T/A will certainly have access to your PNR so it won't be your little secret. If you had booked the ticket yourself at delta.com you would have a better chance of getting away with it.