Bikedued, (at the risk of offending some on this forum), my opinion is its the brand name of the bike you're selling along with the fact that it's not vintage. A lot of folks see "Wally World" with a big, round "Target" when they see Schwinn if the bike is not a vintage roadie from the days when Schwinn ruled. I have to admit, I stay away from their late model MTBs at yard sales for the same reason. I can hear the responses when I consider flipping one "Why should I pay you $125 for a used Schwinn when I can buy a new one at Wally World for $110?".
If you have not already done so, I think you should stress that your bike is a high quality bike sold by a LBS, not a department store Schwinn. Maybe that will help. BTW Mongoose suffers from the same problem. The only two Mongoose LBS MTB's I picked up I stripped for parts. Flipping them is a lost cause no matter how nice they are.