Can't someone build a portfolio by doing demo trading
Usually, a demo trade is not a genuine trade. So the genuity will not be there. For me, I won't like to follow someone's demo trade.
There is difference between a demo trade and live trade, at least seriousness is part of it.
Definitely, the difference is only in the emotion of traders with the fear of losing or the excitement of winning. In demo trading, traders do not get much bothered about the direction of the trade. But I think what "Stedsm" referred to there with demo was for trade practice of anyone interested in trying the service offered by the OP.