About a year ago, I needed to travel BWI to ATL rt. The 21 day advance fare with a Sat stay was about $180. I wasn't staying over a Sat, so the fare would have been $1,000. I asked my travel agent about purchasing two rt's and they booked me that way. First was BWI-ATL-BWI. Second was ATL-BWI-ATL. I used the first leg on each of the two rt's and paid $360.

6 months later, I got a charge from DL for $1,380. The travel agency said it was because of a "tarriff violation". After 6 months of arguing with the agency (they booked the tickets, they should know the rules) they ate the charge from DL.

Got to keep the miles, though