Saberhagen can not be exchanged, as he can be easily obtained from the beginner showdown. Yes, I played through that one multiple times in march so now I have 6 saberhagens 🙂
The live series cards may be due to the fact that in the first couple of weeks non-sellable cards from team packs (2 bronzes and 2 silvers) were not exchangeable. For example, if you pulled Andujar in the Granderson program odds are that you're stuck with his duplicate.
I find that the best time to buy cards cheaply with buy orders is in the early morning. That would be around 9 o'clock central european summer time, or 7 GMT. During the day, the buy now and sell now prices tend to creep closer together.