Considering that the agent has less work, if he/she chooses pax who finish their journey in DTW, I think he/she will pick those guys first.
Touching an internal itenary has always been problematic and after the Sep. 11 related security BS and bla bla I fear it has become even worse...
Reminds of the good old days, when KL and NW used to oversell the MEM-AMS flight without any mercy, giving out up to $ 1000 for a bump on this sector...