I think it would be hard to resell characters, because Cipsoft already takes a good margin in each trade. Even if you search for very good deals, the prices have to be considerably low (40% or more) for you to maintain a good profit. Remember that every char you purchase, you are paying 12% more, and when you sell, you get 12% less, plus the 50tcs you loose. It is also difficult to know the real value of chars. So there is a high chance of misjudging a deal and losing money.
One alternative way to profit is to create multiple level 8 chars in your main account (pacc) and leave them offline training every day. After a while they will have high skills, and you can sell them for a reasonable good amount of tcs.